JAC Class 9 Science Important Questions Chapter 15 Improvement in Food Resources

JAC Board Class 9th Science Important Questions Chapter 15 Improvement in Food Resources

Multiple Choice Questions

Question 1.
Nitrogen, phosphorus, and potassium are examples of …………….
(a) micronutrients
(b) macronutrients
(c) fertilizers
(d) both (a) and (c)
Answer:
(b) macronutrients

Question 2.
Cyprinus and Parthenium are types of …………….
(a) diseases
(b) pesticides
(c) weeds
(d) pathogens
Answer:
(c) weeds

Question 3.
Using fertilisers in farming is an example of …………… .
(a) no cost production
(b) low – cost production
(c) high – cost production
(d) none of these
Answer:
(c) high – cost production

Question 4.
What is the other name for Apis cerana indica?
(a) Indian cow
(b) Indian buffalo
(c) Indian honeybee
(d) None of these
Answer:
(c) Indian honeybee

JAC Class 9 Science Important Questions Chapter 15 Improvement in Food Resources

Question 5.
The management and production of fish is called …………… .
(a) pisciculture
(b) apiculture
(c) sericulture
(d) aquaculture
Answer:
(a) pisciculture

Question 6.
Pasturage is related to …………… .
(a) cattle
(b) fishery
(c) apiculture
(d) sericulture
Answer:
(c) apiculture

Question 7.
What is the process of growing two or more crops in a definite pattern called?
(a) Crop rotation
(b) Intercropping
(c) Mixed cropping
(d) Organic cropping
Answer:
(b) Intercropping

Question 8.
The kharif season extends from …………… .
(a) November to April
(b) June to October
(c) March to November
(d) December to March
Answer:
(b) June to October

Question 9.
For mixed cropping, which of the following combinations of crops is not suitable?
(a) Wheat + maize
(b) Wheat + gram
(c) Wheat + mustard
(d) Groundnut + sunflower
Answer:
(a) Wheat + maize

Question 10.
Catla, Rohu and Mrigals constitute …………… .
(a) marine fishes
(b) brackish water fishes
(c) fresh water fishes
(d) both (a) and (b)
Answer:
(c) fresh water fishes

Analysing & Evaluating Questions

Question 11.
Madhu visited a dairy farm with her friends. There they saw the various kinds of cattle kept in sheds, food given to them and so on. What are the main components of feed provided to the cattle?
(a) Roughage
(b) Concentrates
(c) Water
(d) All of these
Answer:
(d) All of these

Question 12.
Find out the correct sentences.
(i) Hybridisation means crossing between genetically dissimilar plants.
(ii) Cross between two varieties is called interspecific hybridisation.
(iii) Introducing genes of desired character into a plant gives genetically modified crop.
(iv) Cross between plants of two species is called intervarietal hybridisation.
(a) (i) and (iii)
(b) (ii) and (iv)
(c) (ii) and (iii)
(d) (iii) and (iv)
Answer:
(a) (i) and (iii)

Question 13.
The characteristic which is not chosen for selective breeding in dairy animals is
(a) lactation period
(b) resistance to diseases
(c) good shelter
(d) nutritional requirement
Answer:
(c) good shelter

Assertion Reason Questions

Directions: In the following questions, the Assertions and the Reasons have been put forward. Read the statements carefully and choose the correct alternative from the following:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.
(C) The assertion is true but the reason is false.
(D) Both the statements are false.
1. Assertion: Organic matter is important for crop production.
Reason: Organic matter provides major essential nutrients to the plant.
Answer:
(C) The assertion is true but the reason is false.

2. Assertion: Manure is better than fertilisers in maintaining soil fertility.
Reason: Manure improves soil structure and increases the water holding capacity of soil.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

3. Assertion: It is better to grow soyabean with maize in the same field.
Reason: Root nodules of soyabean plants have nitrogen fixing bacteria which enrich the soil with nitrogen.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

4. Assertion: Mixed cropping is a good practice in agriculture.
Reason: By mixed cropping, number of weeds in the field can be reduced.
Answer:
(C) The assertion is true but the reason is false.

5. Assertion: Grains to be stored should have low moisture level.
Reason: Low moisture level in grains inhibits the growth of bacteria and fungi.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

Very Short Answer Type Questions

Question 1.
State one demerit with composite fish culture system.
Answer:
Many fishes breed only during monsoon so hormonal stimulation has to be given. Also, good quality fish seeds are not available.

Question 2.
State one importance of photoperiod in agriculture.
Answer:
Photoperiod in agriculture provides adequate light for flowering.

Question 3.
Name two micronutrients and two macronutrients which plants take from the soil.
Answer:
(a) Macronutrients are: calcium (Ca), magnesium (Mg)
(b) Micronutrients are: boron (B), chloride (Cl)

Question 4.
How does catla differ from mrigal?
Answer:
Catla belongs to genus Catla while mrigal belongs to genus Cirrhinus. Catla is a surface feeder and native to the Northern waters of India while mrigal is a bottom – feeder and native to the Ganges and Brahm putra rivers of India.

JAC Class 9 Science Important Questions Chapter 15 Improvement in Food Resources

Question 5.
Name the two vitamins which are added in the poultry feed.
Answer:
Vitamins A and K.

Question 6.
From where do plants acquire the following nutrients?
(a) Nitrogen
(b) Hydrogen
Answer:
(a) Soil (b) Water

Question 7.
Which nutrients are supplied by cereals and pulses?
Answer:
Carbohydrates and proteins are supplied by cereals and pulses, respectively.

Question 8.
Name any two weeds of crop field.
Answer:
Xanthium (chota dhatura), Parthenium (gajar ghas), Cyperinus rotundus (motha).

Question 9.
Define animal husbandry.
Answer:
Animal husbandry is the practice of management and care of farm animals by humans for profit.

Question 10.
Mention two exam pies of crop combinations that are grown in mixed cropping.
Answer:
Some combinations of mixed cropping are:
(a) Wheat and mustard
(b) Maize and urad (pulse)
(c) Groundnut and sunflower

Question 11.
(a) Name an exotic variety of honeybee grown in India.
(b) What is the rearing of fish on a large scale called?
Answer:
(a) Apis cerana indica
(b) Pisciculture

Question 12.
Name two exotic cattle breeds with long lactation periods?
Answer:
The period of milk production after the birth of a calf is called lactation period. Jersey and Brown Swiss are two exotic cattle breeds having long lactation periods.

Question 13.
Between broiler and layer, which one matures earlier?
Answer:
Broilers have fast growth rate.

Question 14.
State the difference between compost and vermicompost.
Answer:

Compost Vermicompost
The compost is obtained by decomposition of organic waste like animal excreta, plant waste, etc., naturally due to decomposition by bacteria. To fasten the process of decomposition redworms are added to the organic matter to obtain compost.

Question 15.
Name two varieties of food required for milch animals.
Answer:
(a) Food to keep animals healthy,
(b) Food to increase lactation.

Question 16.
Define apiculture.
Answer:
Keeping bee for obtaining honey commercially is called apiculture.

Question 17.
Define hybridisation.
Answer:
Hybridisation refers to crossing between genetically dissimilar plants to obtain better variety of crops.

Analysing & Evaluating Questions

Question 18.
A farmer wants to use a crop variety that can give a good yield. What should he do to select the variety to get the desired result?
Answer:
A good crop yield can be obtained by selecting varieties having useful characteristics such as disease resistance, response to fertilizers and high yields.

Question 19.
A bee – keeper tries to collect a good yield of honey from his apiaries. However, he is unable to collect adequate honey. Suggest him a way to produce more honey.
Answer:
The bee – keeper should maintain his apiaries in between the fields of flowering plants or pasturage. This will allow bees to collect plenty of nectar and pollen from the variety of flowers. Also, the taste of honey depends on the variety of flowers available to the bees.

Question 20.
A dairy farmer wants to maintain a good and clean shelter for his dairy animals. How can he do this so that his animals stay healthy and produce clean milk?
Answer:
The shelter for dairy animals should have following features.

  1. It should be well – ventilated to allow fresh air to enter.
  2. It should have leakage – proof roof to protect them from rain, heat and cold.
  3. The floor of cattle shed should be sloping for easy cleaning and keeping it dry.

Short Answer Type Questions

Question 1.
Distinguish between a mullet and a prawn.
Answer:
Mullet is a type of fish while prawn is a crustacean. Both live in water and serve as a food supplements worldwide. Prawn belongs to the phylum arthropoda, whereas mullet belongs to the group of pisces. So one can use their characteristic features to distinguish between the two.

Question 2.
What are genetically modified (GM) crops?
Answer:
GM (Genetically Modified) crops are the crops in which a gene from some other organism, like another plant or a microorganism, is inserted to get desired characteristics such as disease resistance, response to fertilisers, product quality and high yields. For example, varieties of cotton, maize, papaya, soyabean, sugar beet, squash, etc., have been modified genetically.

Question 3.
Give the technical terms for milk -producing females and farm labour animals.
Answer:
Milk – producing females are called milch animals (dairy animals), while the ones used for farm labour are called draught animals.

JAC Class 9 Science Important Questions Chapter 15 Improvement in Food Resources

Question 4.
Mention the preventive and control measures used before the grains are stored.
Answer:
Cleaning of the produce before storage, proper drying of the produce first in sunlight and then in shade, and fumigation using chemicals that can kill pests.

Question 5.
What is the effect of deficiency of nutrients?
Answer:
Deficiency of nutrients affects physiological processes in plants including reproduction, growth, susceptibility to diseases, yield, etc. General health of the plants depends on the nutrients.

Question 6.
In what way does manure help in soil fertility?
Answer:
Manure helps in enriching the soil with mainly organic matter and small quantities of nutrients. The bulk of organic matter in the form of manure helps in increasing water holding capacity in sandy soil. In clayey soil, the large quantities of organic matter help in drainage and avoiding waterlogging.

Question 7.
Give two advantages of using chemical fertilisers over manure.
Answer:
Two advantages of using chemical fertilisers over manure are as follows:

  1. Chemical fertilisers are ‘nutrient specific’ and can provide specific elements like nitrogen, phosphorus or potassium to the soil in any desired quantity. Manure is, however, not nutrient specific.
  2. Chemical fertilisers, being soluble in water, are readily absorbed by the crops. This is not so in the case of manures.

Question 8.
What is green revolution?
Answer:
Bumper production of cereals (grains) using high-yielding varieties (HYV), higher dose of fertiliser and better modes of irrigation is known as green revolution.

Question 9.
What are pesticides? Give four methods of pest control.
Answer:
Pesticides are the chemicals used to control weeds, insects, rodents, fungi and diseases of plants. They include weedicides, insecticides and fungicides. Some methods of pest control are:

  1. Use of resistant varieties
  2. Optimum time of sowing the seeds
  3. Follow crop rotation and cropping pattern
  4. Deep ploughing of the field in summers to destroy undesirable weeds and pathogens.

Question 10.
Define organic farming.
Answer:
It is the farming in which no chemical fertilisers, pesticides or herbicides are used. It uses all organic matter for the growth of plants like manure, neem leaves as pesticides during grain storage, etc.

Question 11:
What desirable traits are focused to develop hybrids by cross-breeding indigenous and exotic breeds of fowl?
Answer:
Desirable traits are focused to develop hybrids by cross-breeding indigenous and exotic breeds of fowl:

  1. Number and quality of chicks
  2. Dwarf broiler parent for commercial chick production as they require less space and food.
  3. Summer adaptation capacity a tolerance to high temperature
  4. Low maintenance requirements
  5. Reduction in the size of the layer with ability to utilise more fibrous and cheaper diets which are formulated using agricultural by – products.

Question 12.
What decides the quality and quantity of honey production in an apiary?
Answer:
The quality and quantity of honey production in an apiary:

  1. For quality of honey: The pasturage, i.e., the kind of flowers available to the bees for nectar and pollen collection will determine the taste of the honey.
  2. For quantity of honey: Variety of bee used for the collection of honey. For example, A. mellifera is used to increase yield of honey.

Analysing & Evaluating Questions

Question 13.
What would happen if poultry birds are larger in size and have no summer adaptation capacity? In order to get small-sized poultry birds having summer adaptability, what method will be employed?
Answer:
The maintenance of optimum temperature is required for better egg production in poultry farming. The large size of birds with no adaptability to high temperature may cause decline in egg production. To obtain small-size birds with high – temperature adaptability during summer season, cross – breeding of poultry birds for desired characteristics can be done. Small size is also needed for better housing and less feed.

Question 14.
Figure below shows the two crop fields (plots A and B) that have been treated by manures and chemical fertilisers respectively, keeping other environmental factors same. Observe the graph and answer the following questions:
(a) Why does plot B show sudden increase and then gradual decrease in yield?
(b) Why is the highest peak in plot A graph slightly delayed?
(c) What is the reason for the different pattern of the two graphs?
JAC Class 9th Science Solutions Chapter 15 Improvement in Food Resources. 1
Answer:
(a) The addition of chemical fertilisers initially leads to rise in crop yield because of the release of the NPK (nitrogen, phosphorus and potassium) and some other nutrients in high quantity. The gradual decline in yield, as shown in plot B, is due to the continuous use of these fertilisers, which cause killing of useful microbes in the soil and alter the chemical composition of soil.

(b) Manures supply nutrients to the soil slowly, as these contain organic matter in high amount. Therefore, manures enrich the soil with nutrients slowly and continuously for a long time. This is the reason that the highest peak in plot A is delayed but maintained for longer period.

(c) In case of plot A, it indicates that the use of manure remains beneficial for longer duration in terms of crop yield and remains high even when the quantity of manure is increased. In case of plot B, chemical fertilisers when used for longer period cause various problems. The loss of soil fertility occurs due to killing of useful microbes in the soil that reduces decomposition of organic matter.

Long Answer Type Questions

Question 1.
Name two fresh initiatives taken to save water and increase the water availability for agriculture.
Answer:
Two new irrigation systems have been developed to save water and increase the availability of water to the crops.
These are:
1. Drip irrigation system: Here, water is supplied to the roots of the plants directly in a drop wise manner. This prevents unnecessaiy wastage of water.
JAC Class 9th Science Solutions Chapter 15 Improvement in Food Resources. 2
2. Sprinkler system: Here, water is sprinkled over the crops like it happens in rain. So, water is distributed uniformly and absorbed by the soil in a better way.
JAC Class 9th Science Solutions Chapter 15 Improvement in Food Resources. 3

Question 2.
What are the factors for which variety improvement of crop is done?
Answer:
The factors for which variety improvement of crop is done are as follows:

  1. Higher yield: To increase productivity of the crop per acre.
  2. Improved quality: The quality of crop products varies from crop to crop, e.g., protein quality is important in pulses, oil quality in oilseeds, longer shelf life in fruits and vegetables.
  3. Biotic and abiotic resistance: Biotic factors are the diseases, insects and nematodes while abiotic factors are drought, salinity, water logging, heat, cold and frost which affect the crop productivity. Varieties resistant to these factors can increase the crop production.
  4. Change in maturity duration: Shorter maturity period of crop reduces the cost of crop production and makes the variety economical. Uniform maturity makes the harvesting process easy and reduces losses during harvesting.
  5. Wider adaptability: It allows the crops to be grown under different climatic conditions in different areas.
  6. Desirable agronomic characteristics: It increases productivity, (e) g., tallness and profuse branching are desirable characters for fodder crops; while dwarfness is desired in cereals, so that less nutrients are consumed by these crops.

Question 3.
Define manure. What are its three different types?
Answer:
Manure contains large quantities of organic matter and also supplies small quantities of nutrients to the soil. It is prepared by the decomposition of animal excreta and plant waste. It helps in enriching the soil with nutrients and organic matter and increasing soil fertility. On the basis of the kind of biological waste used to make manure, it can be classified into three types:

  1. Compost
  2. Vermicompost
  3. Green manure

1. Compost: It can be farm waste material such as livestock excreta (cow dung, etc.), vegetable waste, animal refuse, domestic waste, sewage, straw, eradicated weeds, etc. These materials are decomposed in pits and this process of decomposition is called composting.

2. Vermicompost: The compost which is made by the decomposition of plant and animal refuse with the help of redworms is called vermicompost.

3. Green manure: Prior to the sowing of the crop seeds, some plants like sun hemp or guar are grown and then mulched by ploughing them into the soil. These green plants thus turn into green manure which helps in enriching the soil in nitrogen and phosphorus.

JAC Class 9 Science Important Questions Chapter 15 Improvement in Food Resources

Question 4.
What are fertilisers? Excessive use of fertilisers is not advisable. Explain.
Answer:
Fertilisers are commercially produced plant nutrients. Fertilisers supply nitrogen, phosphorus and potassium to the crops. They are used to ensure good vegetative growth (leaves, branches and flowers), giving rise to healthy plants. Fertilisers are an important factor in the higher yields of high – cost farming.
Excessive use of fertilisers is not advisable as:

  1. It leads to soil and water pollution.
  2. It can destroy the fertility of soil.

As the soil is not replenished, microorganisms in the soil are harmed by fertilisers.

Question 5.
How does intercropping differ from mixed cropping?
Or
What are the different cropping systems?
Answer:
It includes different ways of growing crops so as to get the maximum benefit. These different ways include the following:
1. Mixed cropping: Mixed cropping is growing two or more crops simultaneously on the same piece of land, e.g., wheat + gram, or wheat + mustard, or groundnut + sunflower. This reduces disease risk and gives some insurance against failure of one of the crops.

2. Intercropping: It involves growing two or more crops simultaneously on the same field in a definite proportion or pattern. A few rows of one crop alternate with a few rows of the other crop, e.g., soyabean + maize, or finger millet (bajra) + cowpea (lobia). The crops are selected such that their nutrient requirements are different. This ensures maximum utilisation of the nutrients supplied and also prevents pests and diseases from spreading to all the plants belonging to one crop in a field. This way, both the crops can give better yield.

3. Crop rotation: The growing of different crops on a piece of land in a pre-planned succession is known as crop rotation. Depending upon the duration, crop rotation is done for different crop combinations. The availability of moisture and irrigation facilities decide the choice of the crop to be cultivated after one harvest. If crop rotation is done properly, two or three crops can be grown in a year with good harvest.

Question 6.
Explain the various methods of irrigation in India.
Answer:
Proper irrigation is very important for the success of crops. Different kinds of irrigation systems include wells, canals, rivers and tanks.

  1. Wells: These are of two types, viz., dug wells and tube wells. In a dug well, water is collected from water bearing strata Tube wells can tap water from the deeper strat(a) From these wells, water is lifted by pumps for irrigation.
  2. Canal system: Water from the main river or reservoir is carried by canal into the field which is divided into branch canals having further distributaries to irrigate the field.
  3. River lift system: In areas where canal flow is insufficient or irregular due to inadequate reservoir release,
    the lift system is more rational. Water is directly drawn from the rivers for supplementing irrigation in areas close to rivers,
  4. Tanks: These are small storage reservoirs which intercept and store the run-off of smaller catchment areas.

Question 7.
Describe the different types of fisheries.
Answer:
The different types of fisheries are marine fisheries, mariculture, inland fisheries, aquaculture and capture fishing.

  1. Marine fisheries: They are caught using fishing nets. Large schools of fishes are located by satellites. Some are farmed in sea water.
  2. Mariculture: They are cultured in seawater. This culture of fisheries is called mariculture.
  3. Inland fisheries: The fisheries in fresh water resources like canals, ponds, reservoirs and rivers are called inland fisheries.
  4. Aquaculture: Culture of fish done in different water bodies is called aquaculture.
  5. Capture fishing: It is the method of obtaining fishes from natural resources, both marine and fresh water.

Question 8.
List six facilities that must be provided to cattle to ensure their good health and production of clean milk.
Answer:
Following facilities must be provided to cattle:

  1. Regular brushing to remove dirt and loosen hair.
  2. Well – ventilated roofed sheds for shelter that can protect them from rain, heat and cold.
  3. The floor of the cattle shed needs to be sloping so as to keep them dry and to facilitate cleaning and spraying of disinfectants at regular intervals.
  4. A balanced diet should be given which contains:
    • roughage which provides high amount of fibre, and
    • concentrate that provides high levels of proteins and other nutrients.
  5. Certain food additives containing micronutrients that promote the health and milk output of dairy animals.
  6. Vaccinations of farm animals, at proper time, against major viral and bacterial diseases.

Analysing & Evaluating Questions

Question 9.
Meena belongs to an agricultural family. She attended a seminar of agricultural practices organised by her school. By listening to the research work of scientists, she learned that spraying pesticides on crops is very harmful for the environment. Next day, she saw the stored tanks of pesticides at her home and told her parents not to use these in excessive quantity.
1. Why are pesticides used in crop fields?
2. What are the various types of pesticides used by the farmers?
3. How can Meena convince her parents to stop using pesticides in large quantities?
4. What alternatives could Meena suggest to her parents instead of using pesticides?
Answer:

  1. The pesticides are used in fields to protect the plants from disease – causing organisms, i.e., bacteria, fungi, viruses, nematodes and mycoplasmas.
  2. Depending on the type of organisms, they destroy, pesticides can be of the following types.
    • Herbicides (for weeds)
    • Insecticides (for insects)
    • Fungicides (for fungi)
    • Bactericides (for bacteria)
  3. Meena can tell her parents that regular and excessive use of pesticides contaminates water and soil, causing pollution in the environment. The pesticides affect the quality of food and leave residues on food items which may affect the health of consumers.
  4. She could suggest the use of biological control methods or use of disease-resistant varieties of crops.

Activity 1
Visit a weed – infested field in the month of July or August and make a list of the weeds and insect pests in the field.

Observations:

  1. Do it yourself.
  2. Weeds are unwanted plants in the cultivated field, e.g., Xanthium (chota dhatura), Parthenium (gajar ghas) and Cyperinus rotundus (motha). They compete for food, space and light.
  3. Some insect pests of crop fields include aphids, blister beetles, common stalk borer, com borer, flour beetle, etc.

Activity 2
Visit a local poultry farm. Observe the types of breeds and note the type of ration, housing and lighting facilities given to them. Identify the layers and broilers.

Observations:

  1. Do it yourself and note down:
    • types of breeds of poultry: Aseel, white Leghorn, Rhode Island Red.
    • types of ration, housing and lighting facilities given to them.
  2. Identify the layers, for example, White leghorn, Rhode Island Red, and broilers, for example, Plymouth Rock or Aseel or any other.

Value Based Questions

Question 1.
A group of eco – club students made a compost pit in the school, they collected all the biodegradable waste from the school canteen and used it to prepare the compost.
1. Name two wastes that can be used for the compost and two wastes obtained from canteen which cannot be used for the compost making?
2. What is the other important component required for making the compost?
3. What values of eco – club students are reflected in this act?
Answer:
The compost:

  1. Two wastes used for compost are vegetable peels and fruit peels. Two waste materials that cannot be used as compost are polythene bags and plastic items.
  2. Bacteria and fungi present in soil are the other important component for making compost.
  3. Eco – club students reflect the value of group work and responsible citizens.

Question 2.
Large number of Bhetki fish died and got crushed in the turbines of hydroelectric power stations while
they migrated from river to sea The environmentalist gave power plant the solution of this problem. Now all Bhetki fish is removed with the help of a special technique and hence do not enter the turbines to crush and die.
1. Suggest two different varieties of fish.
2. What value of environmentalist is reflected in the above case?
Answer:
The turbines to crush and die:

  1. Two varieties of fish are bony and cartilaginous.
  2. Environmentalist showed the value of concern and caring individuals.

JAC Class 9 Science Important Questions

JAC Class 9 Science Important Questions Chapter 14 Natural Resources

JAC Board Class 9th Science Important Questions Chapter 14 Natural Resources

Multiple Choice Questions

Question 1.
Most of the water on the earth’s surface is found in
(a) lakes
(b) rivers
(c) oceans and seas
(d) underground
Answer:
(c) oceans and seas

Question 2.
Ozone hole was first observed over
(a) Antarctica
(b) Australia
(c) Arctic ocean
(d) America
Answer:
(a) Antarctica

Question 3.
Nitrogen fixing bacteria cannot fix N2 in the presence of
(a) CO2
(b) N2
(c) O2
(d) light
Answer:
(c) O2

Question 4.
Which of the following compounds is not degraded by any biological process?
(a) CFCs
(b) CH4
(c) Glucose
(d) Nitrites
Answer:
(a) CFCs

Question 5.
Nitrogen – fixing bacteria are found in the roots of
(a) wheat
(b) maize
(c) pulses
(d) sugarcane
Answer:
(c) pulses

Question 6.
Venus and Mars have no life because
(a) they have no atmosphere
(b) their atmosphere has only oxygen
(c) their atmosphere has 95% – 97% carbon dioxide
(d) their atmosphere has 95% – 97% oxygen
Answer:
(c) their atmosphere has 95%-97% carbon dioxide

Question 7.
Which one of the following organisms are very sensitive to the levels of contaminants like sulphur dioxide in air?
(a) Bacteria
(b) Fungi
(c) Algae
(d) Lichens
Answer:
(d) Lichens

JAC Class 9 Science Important Questions Chapter 14 Natural Resources

Question 8.
Burning of fossil fuels adds
(a) CO2, SO2, NO2 gases in air
(b) C, SO2, N2 gases in air
(c) O2, SO3, NO3 gases in air
(d) H2O, CO2 NO2, gases in air
Answer:
(a) CO2, SO2, NO2 gases in air

Question 9.
Nitrogen fixation can be done by
(a) Industries
(b) Rhizobium
(c) Lightening
(d) All of the above
Answer:
(d) All of the above

Question 10.
On moon the temperature ranges from – 190°C to 110°C. This is due to
(a) absence of water bodies
(b) presence of water bodies
(c) absence of biogeochemical cycles
(d) absence of atmosphere
Answer:
(d) absence of atmosphere

Question 11.
Depletion of ozone molecules in the stratosphere is due to
(a) chlorine compounds
(b) fluorine compounds
(c) halogen compounds
(d) none of these
Answer:
(c) halogen compounds

Question 12.
The life supporting zone of the earth is
(a) lithosphere
(b) hydrosphere
(c) atmosphere
(d) biosphere
Answer:
(d) biosphere

Question 13.
The organism which helps in the formation of soil is
(a) bacterium
(b) moss
(c) lichen
(d) both (b) and (c)
Answer:
(d) both (b) and (c)

Question 14.
The outermost crust of the earth is called
(a) atmosphere
(b) exosphere
(c) lithosphere
(d) hydrosphere
Answer:
(c) lithosphere

Analysing & Evaluating Questions

Question 15.
The atmosphere of the earth is heated by radiations which are mainly
(a) radiated by the sun
(b) re – radiated by land
(c) re – radiated by water
(d) re – radiated by land and water
Answer:
(c) re – radiated by water

Question 16.
The term “water pollution” can be defined in several ways. Which of the following statements does not give the correct definition?
(a) The addition of undersirable substances to water bodies
(b) The removal of desirable substances from water bodies
(c) A change in pressure of the water bodies
(d) A change in temperature of the water bodies
Answer:
(c) A change in pressure of the water bodies

Question 17.
When we breathe in air, nitrogen also goes inside along with oxygen. What is the fate of this nitrogen?
(a) It moves along with oxygen into the cells.
(b) It comes out with the CO2 during exhalation.
(c) It is absorbed only by the nasal cells.
(d) Nitrogen concentration is already more in the cells so it is not at all absorbed.
Answer:
(b) It comes out with the CO2 during exhalation.

Assertion Reason Questions

Directions: In the following questions, the Assertions and the Reasons have been put forward. Read the statements carefully and choose the correct alternative from the following:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.
(C) The assertion is true but the reason is false.
(D) Both the statements are false.
1. Assertion: Plants cannot utilise
nitrogen directly from the atmosphere. Reason: Plants can only use nitrates and nitrites.
Answer:
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.

2. Assertion: Water vapour is not a greenhouse gas.
Reason: Water vapour does not contribute in global warming.
Answer:
(D) Both the statements are false.

3. Assertion: The moon has very cold and very hot temperature variations.
Reason: Moon does not possess the atmosphere.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

4. Assertion: It is easier to fly a kite near a sea shore.
Reason: There is a regular unidirectional wind from sea to land.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

5. Assertion: Legumes revive the soil fertility.
Reason: Microbes in the root nodules of legumes fix atmospheric nitrogen.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

Very Short Answer Type Questions

Question 1.
What is biosphere?
Answer:
The life – supporting zone of earth where atmosphere, hydrosphere and lithosphere interact and make life is known as biosphere.

Question 2.
What are the biotic and abiotic components of biosphere?
Answer:
Abiotic or physical components of biosphere consist of geographical conditions such as the temperature, rainfall, soil, seasons and the climate, while biotic components include animals, plants, fungi and bacteria.

Question 3.
What percentage of oxygen and nitrogen is present in the air?
Answer:
About 21% oxygen and 78% nitrogen is present in the air.

JAC Class 9 Science Important Questions Chapter 14 Natural Resources

Question 4.
Name the air pollutants released by the industries.
Answer:
Industrial air pollutants are sulphur dioxide, carbon dioxide, oxides of nitrogen, hydrogen sulphide, fumes of acids, dust, particles of unbumt carbon, lead, asbestos and even cement.

Question 5.
What are the two factors that cause changes in our atmosphere?
Answer:
(a) Heating of air, and
(b) formation of water vapour.

Question 6.
State any two harmful effects of air pollution.
Answer:
Two harmful effects of air pollution are:
(a) Respiratory problems
(b) Global warming

Question 7.
What is soil?
Answer:
Soil is a mixture of small particles of rocks of different sizes, humus and microscopic life.

Question 8.
State the major source of minerals in the soil.
Answer:
The mineral nutrients present in a particular soil depend on the rocks it was formed from. This means that the major source of minerals in a soil is their parent rocks.

Question 9.
What is top soil?
Answer:
The topmost layer of the soil that contains humus and living organisms in addition to the soil particles is called top soil.

Question 10.
Name two chemicals that are depleting ozone layer.
Answer:
Chlorofluorocarbons (CFCs) and halogenated ozone depleting substance (ODS).

Question 11.
Name two greenhouse gases.
Answer:
Methane and carbon dioxide.

Question 12.
Define nitrification.
Answer:
The biological conversion of ammonia into nitrites and then oxidation of nitrites to nitrates is called nitrification.

Question 13.
Name a nitrogen fixing bacterium.
Answer:
Rhizobium

Question 14.
Define humus.
Answer:
The fertile dark substance present in the topmost layer of the soil which contains dead remains of plants and animal wastes, like excreta, that adds nutrients to the soil is called humus.

Question 15.
What is denitrification?
Answer:
Conversion of nitrates into free nitrogen is called denitrification.

Question 16.
How does carbon exist in all life forms?
Answer:
Carbon is present in all life forms in the form of proteins, carbohydrates, fats, nucleic acids and vitamins.

Question 17.
Name two biologically important compounds that contain both oxygen and nitrogen.
Answer:
Proteins and nucleic acids (DNA and RNA).

Question 18.
Name the two gases given out by the burning of fossil fuels, which dissolve in rain to form acid rain.
Answer:
Sulphur dioxide (SO2) and oxides of nitrogen.

Analysing & Evaluating Questions

Question 19.
A person is burning a huge amount of waste in an open are(a) Which gas is being utilised for burning process and which gas is released into the atmosphere?
Answer:
The process of burning or combustion utilises oxygen and produces carbon dioxide. Thus, oxygen gas is being utilised in the process, and carbon dioxide is released into the atmosphere.

Question 20.
A huge amount of plant and animal waste is being dumped in a lake. What will be the condition of lake after some time?
Answer:
When organic waste (plant and animal residue) is dumped into a water body, the biological oxygen demand of the water increases. This is because the decomposition of organic matter by microorganisms needs more oxygen in water. As a result, there arises oxygen deficiency in water, which leads to the death of other aquatic organisms.

JAC Class 9 Science Important Questions Chapter 14 Natural Resources

Question 21.
Some industries release hot water or very cold water into water sources directly. Why should this be stopped?
Answer:
When excessive hot water or cold water is released into water bodies, it may affect some aquatic organisms. This is because these organisms live in a certain range of temperature and any change in this range (due to the release of excessive hot water or cold water) may cause threat to their survival.

Short Answer Type Questions

Question 1.
The atmosphere acts as a blanket. How?
Answer:
The blanket of atmosphere, which is covering the earth, keeps the average temperature of the earth fairly steady during the day and even during the course of the whole year. The atmosphere prevents the sudden increase in temperature during the daylight hours. And during the night, it slows down the escape of heat into outer space.

Question 2.
What are the consequences of global warming?
Answer:
(a) An increase in temperature of earth even by 1°C may lead to the melting of ice on the poles.
(b) The melting of ice will result in rise of sea level.
(c) Due to rise in sea level, many coastal cities will be flooded or submerged.
(d) Increase in temperature of earth results in change in weather and may cause excessive raining or drought or extreme hot or cold weather conditions.

Question 3.
Name the various organisms involved in nitrogen cycle.
Answer:
(a) Nitrogen fixing bacteria, e.g., Rhizobium, Azotobacter.
(b) Bacteria which convert complex nitrogenous organic compounds (proteins) into ammonia, e.g., Clostridium, Proteus.
(c) Nitrifying bacteria which convert ammonia into nitrates, e.g., Nitrosomonas and Nitrobacter.
(d) Denitrifying bacteria, e.g., Pseudomonas.

Question 4.
What does the presence of smog in an area indicate?
Answer:
The presence of smog in an area indicates the high percentage of smoke released in the air by combustion of fossil fuels in industries, thermal power plants or automobiles. It is an indicator of air pollution.

Question 5.
Write three ways to prevent soil pollution.
Answer:
(a) By judicious use of fertilizers and pesticides.
(b) By proper management of disposal of household waste.
(c) By practising intensive cropping and terrace farming.

Question 6.
How is greenhouse effect related to global warming?
Answer:
Higher concentration of greenhouse gases, such as carbon dioxide, methane, nitrous oxide, etc., in the atmosphere causes absorption of reflected heat and avoids their escape into the space. This phenomenon is called greenhouse effect. This leads to rise in the temperature of earth’s atmosphere throughout the world causing global warming. This global warming caused by greenhouse gases like CO2, CH4, etc., leads to the melting of glacier and polar ice. This would cause rise in the level of sea and other climate changes. Hence, we can say that global warming is a consequence of greenhouse effect.

Question 7.
What is air pollution? How is it caused? Write its two harmful effects.
Answer:
The contamination of air with unwanted gases, particles like dust, etc, which makes it unfit for inhalation is called air pollution.

  • Causes:
    1. (a) Burning of fossil fuels releases SO2, CO2 and NO2 gases.
    2. (b) Burning of fuels releases unbumt carbon particles and smoke.
    3. (c) Smoke from industries and vehicles.
  • Harmful effects:
    1. (a) It causes respiratory problems.
    2. (b) It causes allergies, asthma, cancer and heart diseases.

Question 8.
What is acid rain? Write its harmful effects.
Answer:
The gases released due to combustion of fossil fuels are SO2, NO2 and CO2. These gases remain suspended in the air. When it rains, the rainwater mixes with these gases to form sulphuric acid, nitrous acid, carbonic acid and comes down on the surface of the earth in the form of acid rain.
JAC Class 9th Science Solutions Chapter 14 Natural Resources 1
(a) It corrodes statues, monuments of marble, buildings, etc.
(b) It makes the soil acidic.
(c) It damages crops and plantations.

Question 9.
What is water pollution? Give its causes and harmful effects.
Answer:
When water is contaminated with unwanted substances and chemicals which make it unfit for use and cause diseases, it is called water pollution.

  • Causes:
    1. (a) Sewage from towns, cities is dumped in the water.
    2. (b) Fertilizers, pesticides, insecticides get washed away into the waterbodies from farmlands.
    3. (c) Effluent from industries.
  • Harmful effects:
    1. (a) Polluted water, when consumed, causes many diseases which are water – borne, like cholera, typhoid, etc.
    2. (b) Mercury in salts dumped by industries causes a brain disorder called Minamata disease.
    3. (c) Many life – forms which are susceptible to temperature changes die.

Question 10.
What is the difference between fog and smog? Give two harmful effects of smog.
Answer:
The water vapour present in air when condenses due to very low temperature is called fog. The smoke released in the air, due to burning of fuels, mixes with the fog and forms smog. Harmful effects of smog: It decreases the visibility and causes adverse effect on aeroplane landing, railways and road transport.

Question 11.
State in brief the role of photosynthesis and respiration in carbon-cycle in nature.
Answer:
Photosynthesis is performed by green plants in the presence of sunlight and it converts carbon dioxide into carbohydrates that are utilised by other living organisms through food chain. Oxygen is replenished in nature only through the process of photosynthesis. Oxygen enters the living world through the process of respiration, i.e., it oxidises the food material (glucose molecules) and produces energy and carbon dioxide.

Question 12.
Explain the importance of ozone to mankind.
Answer:
Ozone covers the earth’s atmosphere. It is present in stratosphere. It does not allow the harmful ultraviolet radiations coming from the sun to enter our earth. These ultraviolet radiations cause ionizing effect and can cause cancer and genetic disorder in any life form. The ozone is getting depleted at the South Pole near Antarctica The ozone depletion is due to the halogens like CFCs (Chlorofluorocarbons) released in the air. Chlorine and fluorine react with the ozone and split it, thereby leading to the formation of a big hole called ozone hole.

JAC Class 9 Science Important Questions Chapter 14 Natural Resources

Question 13.
How are winds caused and what decides the breeze to be gentle, strong wind or a terrible storm?
Answer:
Movement of air, terrible storm and rains, all these phenomena are the result of changes that take place in our atmosphere due to the heating of air and the formation of water vapour. Water vapour is formed due to the heating of water bodies and the activities of living organisms. The atmosphere can be heated from below by the radiation that is reflected back or re-radiated by the land or water bodies. On being heated, convection currents are set up in the air. This causes wind. The pressure gradient or the pressure difference determines the speed and intensity of wind. Larger the gradient, more is the wind speed.

Question 14.
Why is step farming common in hills?
Answer:
At hills, the rainwater flows with a very high speed which provides very less time to absorb rainwater into the soil. So, the fields contain wide steps which slow down the speed of fast flowing water. Therefore, farming fields get more chances to absorb rainwater, i.e, more water can seep into the soil for better farming. Besides this, step farming also reduces soil erosion.

Question 15.
Write the harmful effects of ozone layer depletion.
Answer:
Harmful effects of ozone layer depletion are as follows:

  1. Due to depletion of ozone layer, more ultraviolet (UV) radiation will reach the earth. UV radiation causes skin cancer, damage to eyes and immune system.
  2. UV radiation kills microorganisms, such as bacteria, even useful ones.
  3. Ozone layer depletion may lead to variation in rainfall, ecological disturbances and dwindling of good food supply.

Analysing & Evaluating Questions

Question 16.
Rashmi visited her village during summer vacations and found that there is severe shortage of water for villagers and animals.
1. Give reason of water shortage in villages.
2. Why some areas of earth suffer from the problem of water scarcity?
3. What ways can Rashmi suggest to villagers to solve the problem of water shortage?
Answer:

  1. The lack of public water supply in villages is the most prominent reason of water scarcity in villages. Villagers depend on natural sources of water which often dry up due to excessive heat during summer.
  2. The water scarcity occurs due to uneven distribution of freshwater on the earth.
  3. Rainwater harvesting is an effective way to solve the problem of water scarcity in villages as well as in cities. The rainwater can be stored in underground tanks, check dams and recharges the groundwater. This groundwater can be drawn for use at the time of shortage of water.

Question 17.
A farmer followed the practice of sowing cereal crops regularly in his field for several seasons. After sometime, he found decline in cereal production.
(a) What may be the reason for less cereal production in farmer’s field?
(b) How the farmer can increase production in his field?
Answer:
(a) Sowing a same crop regularly in the field for several seasons makes the soil deficient of certain essential nutrients.
Thus, the fertility of soil declines after sometime and the crop production becomes less.

(b) The farmer can grow leguminous crops after cereal crop. The nitrogen fixing bacteria that live in root nodules of legume crops help in replenishment of lost nitrogen in the soil by fixing atmospheric nitrogen.

Long Answer Type Questions

Question 1.
Describe the carbon – cycle in nature.
JAC Class 9th Science Solutions Chapter 14 Natural Resources 2
Answer:
All living things are made of carbon. Carbon is also a part of the oceans, air, and even rocks. Because the earth is a dynamic place, carbon does not stay still. Carbon – cycle is the series of processes by which carbon compounds are interconverted in the environment, involving the incorporation of carbon dioxide into living tissues by photosynthesis and its return to the atmosphere through respiration, the decay of dead organisms and the burning of fossil fuels.

If we see from the beginning, CO2 in the atmosphere is taken by the plants which use it to make glucose, water and oxygen. Also, direct CO2 from air forms carbonates in water which later turns into limestone. Then, these plants are eaten us and other animals, i.e., we indirectly use COus and other animals, i.e., we indirectly use CO2 present in the plants. Also, we respire CO2 back in atmosphere.

Then, organic compounds (plants / animals) form coal and petroleum, or we can say fossil fuel. And also, animal body present in the plants. Also, we respire CO2 back in atmosphere. Then, organic compounds (plants / animals) form coal and petroleum, or we can say fossil fuel. And also, animal body forms inorganic carbonates or shells. But nowadays, we bum fossil fuels too much (and also cut the trees) which is harmful. As a result, we are not getting rid of excess CO2 from our atmosphere.

Question 2.
Why is replenishment of forests necessary?
Answer:
Forests need to be replenished because of the following reasons:

  1. Rainfall: During transpiration, trees give out enormous amount of water vapour. This water vapour helps in the formation of clouds. So, if trees are cut and not replenished, the rainfall in the area will reduce.
  2. Natural rate of tree growth: Forests cannot be re – grown in a few days or months as trees take many years to grow fully. Thus, it becomes necessary to replenish the forests periodically.
  3. Soil erosion: If a large number of trees are cut, the soil becomes naked. The topsoil, which is rich in organic matter will be washed away by water or carried away by wind. Trees help in binding the soil.
  4. Carbon dioxide – oxygen balance: Forests have a very large number of trees which give out 02 and take in C02 by photosynthesis. In this way, they help in maintaining the carbon dioxide-oxygen balance in the atmosphere.
  5. Timber and fuel: Forests are the best suppliers of timber for furniture and fuel. So, for their constant supply, forests need to be replenished.

Question 3.
Draw a labelled diagram to show nitrogen cyclele in nature.
Answer:
Nitrogen exists as free nitrogen in the atmosphere. In air, N2 is about 78%. This free nitrogen is fixed into compounds of ammonia and nitrates. Most of the organisms cannot utilise molecular nitrogen. Fixation of Nitrogen:
Fixation of free nitrogen into compounds takes place by the following means:
1. Certain blue green algae and bacteria can fix atmospheric nitrogen.

2. Nitrogen – fixing bacteria found in the root nodules of legumes such as grams, beans, pulses, etc., fix atmospheric nitrogen into nitrogen containing compounds.

3. Lightning also helps in the formation of nitrogen containing compounds. Nitrogen containing fertilisers produced artificially in factories are the fixed form of nitrogen. Plants take up compounds containing nitrogen from the soil. From plants nitrogen passes into food web Decay of dead plants and animals and excreta like urine, faeces, cause return of nitrogen compounds to the soil. Denitrifying bacteria and fire cause liberation of free nitrogen in the atmosphere.
JAC Class 9th Science Solutions Chapter 14 Natural Resources 3
Importance of Nitrogen – cycle: Nitrogen is an important constituent of tissues, proteins, enzymes, nucleic acids and amino acids. Atmosphere contains about 78 per cent nitrogen but plants and animals cannot use nitrogen in this form. Plants take nitrogen in the form of nitrates, the usable form. From plants, nitrogen travels to animals through food. If nitrogen in the form of proteins, amino acids, enzymes, etc., remains locked up in the bodies of organisms, there will be shortage of usable form of nitrogen. Therefore, circulation of nitrogen in nature is very essential.

Question 4.
Explain the oxygen – cycle in nature.
Answer:
Oxygen is an important component of everyday life. We cannot survive without oxygen. It comprises about 21% of atmospheric air. It is a component of several biological molecules such as carbohydrates, proteins, nucleic acids and fats. Like carbon dioxide, oxygen too is cycled through the process of photosynthesis and respiration. Oxygen is also utilised during combustion or burning.
JAC Class 9th Science Solutions Chapter 14 Natural Resources 4
Oxygen – cycle: Oxygen from the atmosphere is used up in three processes, viz., combustion, respiration and in the formation of oxides of nitrogen.

  1. Animals take in oxygen through the process of respiration. They release CO2 into the atmosphere.
  2. Carbon dioxide, released by animals, is used by plants in the process of photosynthesis.
  3. Plants release oxygen into the atmosphere as a by-product of photosynthesis.
  4. Fuels need oxygen for combustion, so they take oxygen and release CO2 into the atmosphere as a by-product along with other gases.
  5. CO2 is released into the air in the process of decaying of dead animals and plants.
  6. This CO2 is taken up by plants for the process of photosynthesis and O2 is released and this process continues.

Question 5.
Describe water – cycle.
Answer:
Water is one of the most important physical components which is essential for survival of life on the earth. The water from the water bodies on evaporation moves up. As the vapours rise up in the atmosphere they become cooler and condense to form clouds which fall down as rain. Rainwater then passes through rivers and gets collected again in the ocean. The circulation of water in this manner is known as water – cycle. The cycle is also performed by living beings like absorption and transpiration of water by plants and drinking by animals. Animals lose water during respiration and perspiration. They lose water through excretion also.
JAC Class 9th Science Solutions Chapter 14 Natural Resources 5

Analysing & Evaluating Questions

Question 6.
There are several sources like respiration by living organisms, combustion, burning of fossil fuels and forest fires which contribute immensely in the carbon dioxide levels of atmosphere. Despite all these activities, the air contains only a mere fraction of carbon dioxide in it. How does it happen?
Answer:
The level of carbon dioxide does not increase in atmosphere because atmospheric carbon dioxide is fixed continuously in different components by the following ways.

  • The plants ‘fix’ or capture the carbon dioxide and convert it into glucose through the process known as photosynthesis.
  • Animals get their carbon directly by eating plants or indirectly by eating herbivores. Many marine animals use carbonates dissolved in seawater to make their shells.
  • The fossil fuels are also the storehouse of carbon. These are the deposits of organic materials formed from decayed plants and animals deep inside the earth. By exposure to heat and pressure in the earth’s crust over hundreds of millions of years, these dead decaying organisms changed into fossil fuels, such as coal and petroleum.
  • The water rich in carbon dioxide accumulates at the bottom of water bodies and forms limestone or carbonated rocks. It involves a series of chemical reactions that remove carbon dioxide from the atmosphere and deposits it in the form of rocks.

Activity 1

  • Take the following:
    1. (i) a beaker full of water
    2. (ii) a beaker full of soil/sand and
    3. (iii) a closed bottle containing a thermometer.
  • Measure the temperature of all these in shade.
  • Now, keep them in bright sunlight for three hours and measure the temperature of all three vessels.

Observations:

  • The temperature of air is less in shade than the temperature of sand or water.
  • The temperature of water does not rise quickly whereas sand gets heated up easily.
  • The temperature of air in the closed bottle is more than the temperature of air in open. This is because heat received from the sun has no outlet to reflect back the heat radiation. The glass does not allow to escape reflected heat radiations to go out.

Activity 2

  • Place a candle in a beaker or wide mouthed bottle and light it. Light an incense stick and take it to the mouth of the beaker as shown in the figure.
  • Now, keep the incense stick near the edge of the mouth, a little above the candle, and in other regions. Record your observations.

Observations:

  • When the incense stick is kept near the edge of the mouth, the smoke flows inwards towards the flame. The hot air around the candle rises up and cold air from the surroundings rushes in to fill the space. This air rushing inside the beaker brings smoke towards the flame.
  • The smoke rises up along with hot rising air when incense stick is kept a little above the candle.
  • In other places, the smoke from the incense stick rises up and then diffuses in the air.

Activity 3
Take two identical trays and fill them with soil. Plant mustard or green gram or paddy in one of the trays and water both the trays regularly for a few days, till the first tray is covered with plant growth. Now, tilt both the trays and fix them in that position. Make sure that both the trays are tilted at the same angle. Pour equal amount of water gently on both trays such that the water flows out of the trays.
JAC Class 9th Science Solutions Chapter 14 Natural Resources 6
1. Study the amount of soil that is carried out of the trays by the water.
2. Now pour equal amounts of water on both the trays from a height. Pour three or four times the amount that you poured earlier.
3. Study the amount of soil that is carried out of the trays now. Record your observations.

Observations:

  • The tray without vegetation loses more soil and holds more water than the tray that has plants.
  • On pouring water on both the trays from a height, more soil flows along with water in the tray without vegetation.
  • Less amount of soil is washed out earlier than that washed out when water was poured from a height.

Value Based Questions

Question 1.
Sudha saw a child sleeping in a car parked, with closed doors and glasses rolled up, in an open area on a sunny day near the market. She immediately raised an alarm and with the help of police she got the window rolled down.
1. Why was it not safe to keep the doors with window glasses rolled up for a child inside the car?
2. Name two gases that can lead to the above effect.
3. What value of Sudha is reflected in the above act?
Answer:

  1. It was not safe for the child in the car with locked doors and windows rolled up because the sunlight would result in the greenhouse effect in the car. This would increase the temperature in the car and also result in the increase in CO2 level which would lead to suffocation.
  2. Carbon dioxide gas and methane gas can lead to greenhouse effect.
  3. Sudha reflects the value of an aware citizen and responsible behaviour.

JAC Class 9 Science Important Questions Chapter 14 Natural Resources

Question 2.
After doing a project on “save water”, Sumit realised the problem of shortage of drinking water on the earth. Sumit started checking the misuse of water in his vicinity.
1. What is the percentage of drinking water available on the earth?
2. Give any two practices that one should follow to save water.
3. What value of Sumit is reflected in this act?
Answer:

  1. 1% of drinking water is available on the earth.
  2. To save water:
    • Do not use shower to take bath every day, instead use a bucket of water.
    • Mop the floor instead of washing.
    • Sumit showed the value of responsible behaviour and participating citizen.
  3. A project on “save water”, Sumit realised the problem of shortage of drinking water on the earth.

JAC Class 9 Science Important Questions

JAC Class 9 Science Important Questions Chapter 13 Why Do We Fall Ill

JAC Board Class 9th Science Important Questions Chapter 13 Why Do We Fall Ill

Multiple Choice Questions

Question 1.
The disease that affects our lungs is
(a) jaundice
(b) tuberculosis
(c) scabies
(d) herpes
Answer:
(b) tuberculosis

Question 2.
The BCG vaccine provides immunity against
(a) dengue
(b) influenza
(c) ebola
(d) tuberculosis
Answer:
(d) tuberculosis

JAC Class 9 Science Important Questions Chapter 13 Why Do We Fall Ill

Question 3.
Malaria is caused by
(a) Anopheles mosquito
(b) Bacteria
(c) Protozoa
(d) Virus
Answer:
(a) Anopheles mosquito

Question 4.
Trypanosoma, Leishmania and Plasmodium are the examples of
(a) protozoa
(b) worms
(c) fleas
(d) viruses
Answer:
(a) protozoa

Question 5.
Diarrhoea, cholera, typhoid are the diseases that have one thing in common, which is
(a) all of them are air-borne
(b) all of them are caused by a virus
(c) all of them are caused by contaminated food and water
(d) all of them cause headache
Answer:
(c) all of them are caused by contaminated food and water

Question 6.
HIV virus attacks which one of the following cells in our body?
(a) Liver cells
(b) Neurons
(c) Nephrons
(d) White blood cells
Answer:
(d) White blood cells

Question 7.
Pathogens of disease are
(a) viruses
(b) bacteria
(c) protozoa
(d) all of the above
Answer:
(d) all of the above

Question 8.
Which of the following is a worm – caused disease?
(a) Herpes
(b) Filariasis
(c) Rabies
(d) Conjunctivitis
Answer:
(b) Filariasis

Question 9.
Which of the following is not a viral disease?
(a) AIDS
(b) Rabies
(c) Polio
(d) Tuberculosis
Answer:
(b) Rabies
(d) Tuberculosis

JAC Class 9 Science Important Questions Chapter 13 Why Do We Fall Ill

Question 10.
Which of the following is caused by Plasmodium parasite?
(a) Hepatitis
(b) Jaundice
(c) Tuberculosis
(d) Malaria
Answer:
(d) Malaria

Analysing & Evaluating Questions

Question 11.
If you live in an overcrowded and poorly ventilated house, you may probably suffer from which of the following diseases?
(a) Cancer
(b) AIDS
(c) Air-borne diseases
(d) Cholera
Answer:
(c) Air – borne diseases

Question 12.
During infection or injuries, inflammation of body organs occurs due to the activation of
(a) nerves
(b) muscles
(c) immune system
(d) breathing
Answer:
(c) immune system

Question 13.
Suppose you are experiencing the symptoms of cough and breathlessness. Which organ of your body do you think might be affected?
(a) Kidney
(b) Lung
(c) Heart
(d) Stomach
Answer:
(b) Lung

Assertion-Reason Questions

Directions. In the following questions, the Assertions and the Reasons have been put forward. Read the statements carefully and choose the correct alternative from the following.
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.
(C) The assertion is true but the reason is false.
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

1. Assertion: DPT is a triple antigen.
Reason: DPT is administered against three diseases namely diphtheria, pertussis and tetanus.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

2. Assertion: Antibiotics are effective against both the bacteria and the viruses.
Reason:  Viruses have many biochemical mechanisms of their own.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

3. Assertion: Male Anopheles mosquitoes do not spread malaria.
Reason: Male Anopheles mosquitoes do not feed on human blood.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

4. Assertion: Typhoid spreads through contaminated food and water.
Reason: Typhoid can never become an epidemic in a locality.
Answer:
(C) The assertion is true but the reason is false.

5. Assertion: HIV attacks the immune system of a person.
Reason: HIV is responsible for AIDS in people infected with it.
Answer:
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.

Very Short Answer Type Questions

Question 1.
What do you understand by symptoms of a disease?
Answer:
Symptoms are the signs of a disease which indicate the presence of that particular disease.

Question 2.
What are acute diseases?
Answer:
Acute diseases are diseases that last for a very short period of time.

Question 3.
What are chronic diseases?
Answer:
Chronic diseases are diseases that last for a very long period of time.

Question 4.
What are infectious diseases?
Answer:
Infectious diseases are diseases that can spread from an infected person to another healthy person, e. g., ebola.

Question 5.
Name any one disease caused due to genetic abnormality.
Answer:
Sickle-cell anaemia.

Question 6.
Name two diseases caused by protozoa.
Answer:
Trichomoniasis and malaria.

JAC Class 9 Science Important Questions Chapter 13 Why Do We Fall Ill

Question 7.
Name two diseases each caused by bacteria, viruses and fungi.
Answer:
Bacteria – typhoid, cholera; Viruses – ebola, mumps; Fungi – Jock-itch, ringworm.

Question 8.
Write the full form of AIDS.
Answer:
Acquired Immunodeficiency Syndrome.

Question 9.
Which organism causes sleeping sickness?
Answer:
A protozoan called Trypanosoma causes sleeping sickness.

Question 10.
Name the causative agent of kala – azar?
Answer:
Leishmania.

Question 11.
Name two air-borne diseases.
Answer:
Anthrax and smallpox.

Question 12.
Name two organ specific diseases.
Answer:
Autoimmune hepatitis which affects the liver and Grave’s disease which affects the thyroid.

Question 13.
Which virus is responsible for AIDS?
Answer:
HIV virus is responsible for AIDS.

Question 14.
State the organs affected by the following diseases. jaundice, malaria, typhoid.
Answer:
Jaundice: liver; malaria – liver and RBCs; typhoid – infects the blood.

Question 15.
How do we kill microbes that enter our bodies?
Answer:
We kill disease: causing microbes with the help of medicines that block the synthesis pathways of microbes.

Question 16.
What are disease specific means of prevention?
Answer:
Disease specific means of prevention is the use of vaccine which prevents specific diseases from affecting us, e.g., tetanus vaccine, rabies vaccine, etc.

Question 17.
Why is the creation of antiviral drugs hard?
Answer:
Viruses grow inside the host and use the host cell machinery and pathways for all its biological processes. Hence, antibiotics are not able to target the virus-specific pathways. Moreover, viruses can alter their mechanisms at a very high rate, so it becomes difficult to target a specific mechanism.

Analysing & Evaluating Questions

Question 18.
Suppose your friend is suffering from severe cold and it makes him sneeze frequently heavily. What would you suggest him as a precautionary measure so that you do not become infected with the disease?
Answer:
Severe cold or cough are airborne diseases which spread through inhalation of respiratory droplets that are released by sneezing and coughing by an infected individual. Therefore, I would suggest my friend to cover his mouth while sneezing or coughing so that virus responsible for causing this disease does not infect others.

Question 19.
A person is suffering from fever and headache from quite a period of time. He is suspecting that it may be typhoid. What should he do to confirm whether it is the same disease?
Answer:
Confirmation of a particular disease can be done by undergoing proper medical check up and laboratory tests under the supervision of a doctor.

Question 20.
Suppose a person is suffering from jaundice. Whether prescribing him penicillin will be useful or not? Name the target organ for jaundice.
Answer:
No, penicillin would not be useful in the treatment of jaundice because it is a viral diseases. Target organ for jaundice is liver.

Short Answer Type Questions

Question 1.
Define health, disease, pathogens and antibiotics.
Answer:
Health. It is a state of mental, physical and social well-being.
Disease. It is the deviation from the normal healthy well-being of an individual.
Pathogens. They are disease-causing microbes, e.g., bacteria, worms, fungi, etc.
Antibiotics. These are drugs that block the biochemical pathways important to bacteria, thereby killing them.

Question 2.
What are the two main causes of a disease?
Answer:
The two main causes are immediate and contributory causes. Immediate cause-this is due to pathogens entering our bodies. Contributory cause-these are the secondary factors which allow these pathogens to enter our bodies through dirty water, contaminated food, infected surroundings, etc.

Question 3.
Define and give examples of vaccines.
Answer:
Vaccine is an antigenic substance prepared from the agent causing the disease, which is given in advance to a body to provide immunity against that specific disease, e.g., chickenpox vaccine, hepatitis vaccine, polio vaccine.

Question 4.
What is antibiotic penicillin? Give its function.
Answer:
Penicillin is a drug prepared from the fungus Penicillium, which does not allow bacteria to build its protective cell wall, thus it dies off easily. It is used to cure diseases and infections caused by bacteria.

Question 5.
A bacterium is a cell which is destroyed by an antibiotic. Our body is also made up of cells. How come antibiotics do not affect our bodies as well?
Answer:
An antibiotic blocks the biochemical pathway through which bacteria build a protective cell wall. Human body cells do not have this cell wall, so antibiotics cannot have any such effect on our body.

JAC Class 9 Science Important Questions Chapter 13 Why Do We Fall Ill

Question 6.
How can cholera become an epidemic in a locality?
Answer:
Cholera is a communicable disease that spreads through contaminated water and food. Let’s say, a person living in a locality contaminates the local water supply with cholera through his excreta. Now, all the people of that locality who drink that water will get infected with cholera.

Question 7.
Why are sick patients asked to take bed rest?
Answer:
Sick patients are asked to take bed rest so that they can conserve their energy which can be used to heal their recovering organs. Moreover, if they move around, there are higher chances of them getting infected with other diseases as their immune system is already weak.

Question 8.
Write a short note on malaria, its symptoms and control.
Answer:
Malaria is caused by a protozoan that lives in blood. The parasite enters our bodies when a female Anopheles mosquito, having the protozoa named Plasmodium, sucks our blood. This protozoan affects our liver and blood cells.

  • Symptoms: muscular pain, headache and very high fever.
  • Control: keeping the surroundings clean with no stagnant water, using mosquito repellents, use of quinine drug.

Question 9.
What is AIDS? How does a person contract AIDS?
Answer:
AIDS or Acquired Immunodeficiency Syndrome is a disease caused by the Human immuno deficiency virus. A person with AIDS has severely affected immune system. Hence, he or she dies from other diseases that thrive from the lack of Acquired WBCs in the HIV infected body.
A person contracts AIDS in the following ways:

  1. Blood transfusion
  2. Sexual intercourse
  3. From infected mother to a baby (in the womb)
  4. Sharing of needles with infected people
  5. Breast feeding (if the feeder is infected).

Question 10.
Becoming infected by an infectious microbe does not always develop into a disease. Why?
Answer:
This is because our immune system is always active and when foreign particles (microbes) enter our body, the immune system instantly attacks it, trying to kill it. So, in cases where our immune system is successful in killing the infectious microbe, we don’t develop the disease it was supposed to cause.

Question 11.
(a) Why is a balanced diet necessary for maintaining a healthy body?
(b) Name two diseases caused by junk food.
Answer:
(a) A balanced diet provides all the nutrients required by our body in the correct amount. It helps to keep our immune system healthy,

(b) Two diseases caused by junk food are obesity and high blood pressure.

Analysing & Evaluating Questions

Question 12.
No polio cases have been reported from India since the last three years. On that basis, WHO has presented certification of poliofree status to India.
1. Which pathogen is responsible for causing polio in children?
2. How the principle of immunisation is implemented for eliminating polio?
3. What is OPV?
Answer:

  1. Poliomyelitis virus.
  2. Oral vaccines for polio are given periodically to children under five years to age to eliminate the occurrence of the disease. These vaccines are the preparations of weak forms of polio virus strains. These preparations stimulate the body to produce antibodies in response to the exposure to polio viruses. Thus, body becomes immune to the polio disease.
  3. Oral Polio Vaccine.

Question 13.
Sachin’s younger brother was suffering from diarrhoea and vomiting. So he made Oral Rehydration Solution (ORS) and gave it to his brother to drink frequently. Then he thought to take him to the doctor for medical checkup.
1. What may be the cause of diarrhoea and vomiting?
2. Name the causative agents for these diseases?
3. Why Sachin gave ORS to his brother?
Answer:

  1. Diarrhoea and vomiting may occur due to the consumption of contaminated food and water.
  2. The causative agents for these are mainly bacteria, but some protozoa and viruses can also cause diarrhoea and vomiting.
  3. Due to diarrhoea and vomiting, the body loses excess of water and other salts leading to dehydration of the body. Therefore, Sachin used his knowledge to save his brother from the discomfort of dehydration by giving him ORS.

Long Answer Type Questions

Question 1.
If someone in the family gets an infectious disease, what precautionary steps will you take to help that person recover fast and prevent other family members from getting infected?
Answer:
(a) The infected person should be kept isolated in a separate room.
(b) The surroundings and the house need to be kept clean.
(c) His (the patient) clothes and utensils should be sanitised regularly.
(d) Separate towels, sheets and blankets should be used by the patient.
(e) Clean and boiled drinking water should be given to the patient.
(f) A balanced and nutritious meal should be provided to the patient.
(g) The patient should be allowed enough rest to recover fully.

Question 2.
What are the different methods used for the treatment and prevention of diseases?
Answer:
Principles of treatment for diseases are:
(a) To reduce the symptoms of the disease.
(b) To kill the cause of the disease, i.e., to kill the disease-causing microbes like bacteria, fungi, protozoa.

Principles of prevention are:
(a) General ways: It relates to preventing exposure to the microbes, which can be done in the following ways.

  1. For air – borne infections. Avoid public spaces, cover your nose while coughing and sneezing.
  2. For water – borne infections. Drink safe and filtered water.
  3. For vector – borne diseases. Keep the surroundings clean, cover your food and water, do not allow stagnant water to collect.
  4. Self – immunity. Exercise regularly to keep your immune system strong.

(b) Specific ways: By getting vaccination, regular checkups and medications.

JAC Class 9 Science Important Questions Chapter 13 Why Do We Fall Ill

Question 3.
State the mode of transmission for the following diseases. malaria, AIDS, jaundice, typhoid, cholera, rabies, tuberculosis, diarrhoea, hepatitis, influenza.
Answer:

Disease Mode of transmission
1. Malaria Mosquito bite (female Anopheles mosquito)
2. AIDS Infected blood, semen, mother’s milk, sharing needle of an infected person
3. Jaundice Contaminated water
4. Typhoid Contaminated food and water
5. Cholera Contaminated food and water
6. Rabies Bite of a rabid animal
7. Tuberculosis Cough and sneeze droplets
8. Diarrhoea Contaminated food and water
9. Hepatitis Contaminated food and water
10. Influenza Cough and sneeze droplets

Question 4.
(a) What causes chickenpox?
(b) State a few precautionary measures for it.
Answer:
(a) Chickenpox is caused by a virus called varicella-zoster virus,
(b) Some precautionary steps for chicken pox are.

  • The infected person should avoid direct contact with people.
  • His clothes should be soaked in boiling water before washing so as to kill the virus.
  • Vaccination should be taken in advance to prevent the disease.

Analysing & Evaluating Questions

Question 5.
Children living in slum areas frequently suffer from symptoms such as abdominal pain, diarrhoea, loose motions, vomiting and loss of appetite.
(a) Name the target organ or organ system for the occurrence of these symptoms.
(b) Why children are frequently suffering from these symptoms?
(c) What should be done to improve the health status of these children?
Answer:
(a) The target organ or organ system for the occurrence of these symptoms is alimentary canal.

(b) These symptoms appear frequently in the children because they live in unhygienic environment where there is non availability of clean drinking water. Hence, making them prone to infections of alimentary canal.

(c) The local authorities responsible for providing public health services should be informed regarding these health problems in the children. There should be provision of clean drinking water supply and proper sanitation in the area, so that the spread of water-borne infections can be prevented.

Activity 1

  • Find out what provisions are made by your local authority (Panchayat/ Municipal Corporation) for the supply of clean drinking water.
  • Find out if all the people in your locality are able to access this.

Observations:

  • Local authority, i.e., Municipal Corporation of our area recycles the water. Used water is treated in water treatment plants, chlorinated and supplied through pipes to people. Water taken from river is also cleaned and made potable.
  • People, who live outside municipal limits use underground water, which is supposed to be safe, by drawing water through handpumps, wells and tube-wells.

Activity 2

  • Rabies virus is spread by the bite of infected dogs and other animals. There are anti-rabies vaccines for both humans and animals.
  • Find out the plan of your local authority for the control of rabies in your neighbourhood. Also find if these measures are adequate or not. Suggest some improvements.

Observations:

  • Local authorities have plan to provide free anti-rabies vaccination at health centres, dispensaries, etc., and also catch the stray dogs. But animal loving organisations force to let them free. Pet owners are required to get anti-rabies vaccination to their dogs/ cats. But this rule is not strictly followed.
  • Suggestions.
    • People should be educated through campaigns about anti-rabies vaccination for both humans and animals.
    • Stray dogs/cats/other animals should be provided with anti-rabies vaccination.
    • Pet owners should be strictly instructed to get themselves and their pets vaccinated against rabies.

Value Based Questions

Question 1.
Radha’s brother, who is 5 years old, had high fever for two days. Doctor prescribes him antibiotics. Radha hesitantly asks for the name of the disease his brother had and why he was advised to take antibiotics without any diagnosis.
1.  Is fever a disease?
2. What is the role of antibiotics?
3. What values of Radha are reflected in the above act?
Answer:

  1. Fever is not a disease; it is a symptom.
  2. Antibiotics are medicines advised to be taken only when the immune system of a patient is unable to fight against the microbes.
  3. Radha showed moral responsibility and general awareness.

Question 2.
Jyoti was suffering from chickenpox and was advised to stay at home by her doctor. Jyoti’s friend persuades her to go for class picnic along with her and have fun. But Jyoti refuses and stays at home.
1. What is the cause of chickenpox?
2. Give one precaution for it.
3. What value of Jyoti is reflected in not going for picnic?
Answer:

  1. Virus causes chickenpox.
  2. One precaution for avoiding spread of chickenpox is to stay away from public places when one is suffering from it and take vaccination.
  3. Jyoti showed moral responsibility and self-awareness.

JAC Class 9 Science Important Questions

JAC Class 9 Science Important Questions Chapter 12 Sound

JAC Board Class 9th Science Important Questions Chapter 12 Sound

Multiple Choice Questions

Question 1.
Which part of the human ear converts sound vibrations into electrical signals?
(a) Malleus
(b) Incus
(c) Tympanic membrane
(d) Cochlea
Answer:
(d) Cochlea

Question 2.
What do dolphins, bats, and tortoises use to hear the sound?
(a) Ultrasound
(b) Infrasound
(c) Both (a) and (b)
(d) None of these
Answer:
(a) Ultrasound

Question 3.
Children under the age of 5 can hear upto
(a) 25 Hz
(b) 25 kHz
(c) 20 Hz
(d) 20 kHz
Answer:
(b) 25 kHz

JAC Class 9 Science Important Questions Chapter 12 Sound

Question 4.
Multiple reflections of sound are used in
(a) stethoscope
(b) trumpet
(c) megaphone
(d) all of these
Answer:
(d) all of these

Question 5.
To hear a distinct echo, the time interval between the original sound and the reflected sound must be at least
(a) 0.2s
(b) 1s
(c) 2s
(d) 0.1s
Answer:
(d) 0.1s

Question 6.
Speed (v), wavelength (l) and the frequency (v) of a sound wave are related as
(a) λ = v × λ
(b) v = λ – v
(c) v = λ × v
(d) v = λ/v
Answer:
(c) v = λ × v

Question 7.
Speed of sound depends upon
(a) temperature of the medium
(b) density of the medium
(c) temperature of source producing sound
(d) temperature and density of the medium
Answer:
(d) temperature and density of the medium

Question 8.
Using which characteristic of sound can we distinguish between the sounds having same pitch and loudness?
(a) Tone
(b) Note
(c) Pitch
(d) Timber
Answer:
(d) Timber

Question 9.
Loud sound can travel a larger distance, due to
(a) higher amplitude
(b) higher energy
(c) higher frequency
(d) higher speed
Answer:
(a) higher amplitude

Question 10.
A wave in slinky travelled to and fro in 5 s. The length of the slinky is 5 m. What is the velocity of the wave?
(a) 10 m/s
(b) 5 m/s
(c) 2 m/s
(d) 25 m/s
Answer:
(b) 5 m/s

Question 11.
The reciprocal of frequency is
(a) amplitude
(b) wavelength
(c) time – period
(d) wave velocity
Answer:
(c) time – period

Question 12.
To and fro motion of an object is called
(a) wave
(b) vibrations
(c) amplitude
(d) all of the above
Answer:
(b) vibrations

Question 13.
Which of the following frequencies will be audible to the human ear?
(a) 5 Hz
(b) 5000 Hz
(c) 27000 Hz
(d) 50000 Hz
Answer:
(b) 5000 Hz

Question 14.
If the distance between a crest and its consecutive trough is L, then the wavelength of the wave is given by
(a) L
(b) 2L
(c) L/2
(d) 4L
Answer:
(b) 2L

Question 15.
What is the nature of the ocean waves in deep water?
(a) Transverse
(b) Longitudinal
(c) Both transverse and longitudinal
(d) None of these
Answer:
(c) Both transverse and longitudinal

Analysing & Evaluating Questions

Question 16.
A key of a mechanical piano is struck gently and then struck again but much harder this time. In the second case
(a) sound will be louder but pitch will not be different
(b) sound will be louder and pitch will also be higher
(c) sound will be louder but pitch will be lower
(d) both loudness and pitch will remain unaffected
Answer:
(a) sound will be louder but pitch will not be different

JAC Class 9 Science Important Questions Chapter 12 Sound

Question 17.
Which kind of sound is produced by an earthquake before the main shock wave begins?
(a) ultrasound
(b) infrasound
(c) audible sound
(d) none of these
Answer:
(b) infrasound

Question 18.
Before playing the orchestra in a musical concert, a sitarist tries to adjust the tension and pluck the string suitably. By doing so, he is adjusting
(a) intensity of sound only
(b) amplitude of sound only
(c) frequency of the sitar string with the frequency of other musical instruments
(d) loudness of sound
Answer:
(c) frequency of the sitar string with the frequency of other musical instruments

Assertion Reason Questions

Directions: In the following questions, the Assertions and the Reasons have been put forward. Read the statements carefully and choose the correct alternative from the following:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.
(C) The assertion is true but the reason is false.
(D) Both the statements are false.
1. Assertion:
Sound travels as a longitudinal wave in air.
Reason: Sound wave needs a medium for its propagation.
Answer:
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.

2. Assertion: Speed of sound increases on increasing the temperature of the medium through which its propagates.
Reason: On increasing the temperature, kinetic energy of the particles of medium increases.
Answer:
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.

3. Assertion: Stage of an auditorium has a curved sound board behind the stage.
Reason: Curved wall spreads sound in all directions evenly.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

4. Assertion: Sound travels faster in solids than in liquids.
Reason: Particles of solids are closely packed as compared to those of liquids.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

5. Assertion: Pitch of a sound wave depends on its frequency.
Reason: Higher the frequency, lesser is the pitch of the sound wave.
Answer:
(C) The assertion is true but the reason is false.

Very Short Answer Type Questions

Question 1.
What is SONAR?
Answer:
SONAR (Sound Navigation And Ranging) is a technique used for determining water depth and locating underwater objects, such as reefs, submarines and school of fish.

Question 2.
Define one hertz.
Answer:
One hertz is one vibration per second.

Question 3.
Name the two types of mechanical waves.
Answer:
The two types of mechanical waves are:

  1. Transverse wave
  2. Longitudinal wave

Question 4.
What is a wave?
Answer:
A wave is a disturbance that travels in a medium due to repeated periodic motion of particles about their mean position, such that the disturbance is handed over from one particle to the other without the actual movement of the particles of the medium.

Question 5.
What is a longitudinal wave?
Answer:
It is a wave in which the particles of the medium vibrate in the direction of propagation of the wave.

Question 6.
What is a transverse wave?
Answer:
It is a wave in which the particles of the medium vibrate perpendicular to the direction of propagation of the wave.

Question 7.
What do you understand by the term ‘echo’?
Answer:
The sound heard after reflection from a rigid obstacle back to the listener is called ‘echo’.

Question 8.
What is ‘pitch’?
Answer:
The way our brain interprets the frequency of an emitted sound is called ‘pitch’.

Question 9.
What is ‘note’ of a sound?
Answer:
The sound produced due to a mixture of several frequencies is called a ‘note’.

Question 10.
What are ‘ultrasonic’ and ‘infrasonic’ sound waves?
Answer:
Sound waves with frequencies below the audible range (less than 20 Hz) are termed as ‘infrasonic sound waves’ and sound waves with frequencies above the audible range (more than 20,000 Hz) are termed as ‘ultrasonic sound waves’.

Analysing & Evaluating Questions

Question 11.
The speed of sound in vulcanised rubber is much lower than in the common solids. Give a proper explanation.
Answer:
Rubber is soft, porous and sound absorber.

Question 12.
A sound wave corresponds to larger number of compressions and rarefaction passing through a fixed point per unit of time. Should it have higher pitch or lower pitch?
Answer:
Such a sound wave will have higher pitch, (i.e., higher frequency).

Question 13.
An echo is heard on a day when temperature is about 22°C. Will the echo be heard sooner or later if the temperature falls to 4°C?
Answer:
At lower temperature, the speed of sound will decrease. Therefore, to travel through the same distance, it will take more time. So the echo will be heard later.

Short Answer Type Questions

Question 1.
What are mechanical or elastic waves? Give examples.
Answer:
The waves which require a material medium for their propagation are called f mechanical waves. They are also called elastic waves because their propagation depends on the elastic properties of the medium.

Examples of mechanical waves:
(a) Sound waves in air.
(b) Waves over water surface.
(c) Waves produced during earthquake (seismic waves).

JAC Class 9 Science Important Questions Chapter 12 Sound

Question 2.
What are electromagnetic waves? Cite examples.
Answer:
The waves which do not require a material medium for their propagation are called electromagnetic waves. Such waves travel through vacuum with a speed of 3 × 108 m/s.
Examples of electromagnetic waves:
(a) Light waves
(b) X – rays
(c) Radio waves
(d) Microwaves

Question 3.
Define ‘crests’ and ‘troughs’ of a wave.
Answer:
In transverse waves, the particles of the medium which have maximum displacement in the positive Y – direction are called ‘crests’ while those which have maximum displacement in the negative Y – direction are called ‘troughs’.

Question 4.
Define the terms ‘compressions’ and ‘rarefactions’.
Answer:
When longitudinal waves pass through a medium, these cause pressure variations in different parts of the medium. The regions of increased pressure are called ‘compressions’ and the regions of decreased pressure are called ‘rarefactions’.

Question 5.
Differentiate between sound and light waves.

Sound wave Light wave
(a) Travels in the form of longitudinal wave. (a) Travels in the form of transverse wave.
(b) Requires a medium for its propagation. (b) Does not require a medium for its propa – gation.
(c) Travels through air with a speed of 332 m/s at 0°C. (c) Travels through air with a speed of nearly 3 × 108 m/s.

Question 6.
Why are the longitudinal waves also called pressure waves?
Answer:
Longitudinal waves travel in a medium as a series of alternate compressions and rarefactions, i.e., as they travel, there is a variation in pressure across the medium. Therefore, they are called pressure waves.

Question 7.
Derive a relation between wavelength, frequency and velocity of a wave.
Answer:
Frequency, wavelength and wave velocity are related as follows: Wavelength is the distance travelled by the wave during the time a particle of the medium takes to complete one vibration. Therefore, if λ be the wavelength and T be the time – period, the wave travels a distance λ in time T.
Hence, Wave velocity = \(\frac{Distance}{Time}\)
⇒ v = \(\frac{\lambda}{\mathrm{T}}\)
⇒ v = λ v
∵ {\(\frac{1}{T}\) = frequency (v)}
∴ Wave velocity = Frequency × Wavelength
The wave velocity in a medium remains constant under the same physical conditions.

Question 8.
On what factor does the frequency of a wave depend?
Answer:
Frequency of a wave is given by,
v = \(\frac{\mathrm{v}}{\lambda}\)
Where,
v is the speed with which the wave propagates, and λ is the wavelength of the wave. Different sources produce oscillations of different frequencies depending on the wavelength of the sources. Frequency changes such that the speed remains constant.

Question 9.
A boat at anchor is rocked by waves whose consecutive crests are 100 m apart. The wave velocity of the mocking crests is 20 m/s. What is the frequency of rocking of the boat?
Answer:
Wavelength, λ = Distance between two successive crests = 100 m
Velocity, v = 20 m/s
Frequency, v = \(\frac{\mathrm{v}}{\lambda}\) = \(\frac{20}{100}\) = 0.20 Hz.

Question 10.
Why do the animals behave in apeculiar manner before an earthquake?
Answer:
When the earthquake strikes, it produces low frequency infrasounds before the main shock waves. These infrasonic waves are not audible to the human ears. But animals are able to detect these waves and hence some animals get disturbed before earthquakes and start behaving in a different manner.

JAC Class 9 Science Important Questions Chapter 12 Sound

Question 11.
Differentiate between longitudinal wave and transverse wave.
Answer:

Longitudinal wave Transverse wave
(a) It needs a medium for propagation. (a) It may or may not need a medium for propagation.
(b) Particles of the medium move in a direction parallel to the direction of propagation of the disturbance. (b) Particles of the medium move in a direction perpendicular to the direction of propagation of the disturbance.
Example: Sound wave. Examples: Light wave and seismic wave.

Question 12.
What are multiple echoes? Give examples.
Answer:
The successive reflection of a sound wave from a number of obstacles results in hearing the echo of the sound transmitted one after the other. When a sound is repeatedly reflected between two parallel distant buildings or cliffs, multiple echoes are produced. For example, rolling of thunder is due to successive reflections between clouds and land surfaces.

Question 13.
A sound wave causes the density of air at a place to oscillate 1200 times in 2 minutes. Find the time period and frequency of the wave.
Answer:
Frequency = \(\frac{1200}{2 \times 60}\) = 10 Hz.
Time period = ?
Frequency = \(\frac{1}{\mathrm{~T}}\)
T = \(\frac{1}{Frequency}\) = \(\frac{1}{10}\) = 0. 1s.

Analysing & Evaluating Questions

Question 14.
The speed of certain waves depends on the source and the medium through which they travel.
1. What kind of waves are these?
2. Give one example of the answer to (a).
Answer:

  1. These waves are mechanical waves.
  2. Sound waves, water waves, string waves are mechanical waves.

Question 15.
The sound of an explosion on the surface of a lake is heard by a boatman 100 m away and by a diver 100 m below the point of explosion.
1. Who will hear the sound of explosion first?
2. If sound takes time t seconds to reach the boatman, how much time (approximately) will it take to reach the diver?
Answer:
1. The diver who is 100 m below the point of explosion will hear the sound of explosion first because sound travels much faster in water than in air.

2. Time taken by sound to reach the diver
= \(\frac{ Speed of sound in air × t}{Speed of sound in Water }\)
= \(\frac{344 \mathrm{~m} \mathrm{~s}^{-1}}{1533 \mathrm{~m} \mathrm{~s}^{-1}} \times \mathrm{ts}\)
= 0.22 t seconds

Long Answer Type Questions

Question 1.
State the factors on which the speed of sound in a gaseous medium depends.
Answer:
The speed of sound in a gas depends on the following factors:
(a) Effect of density: At constant pressure, the speed of sound in a gas is inversely proportional to the square root of its density.
Speed of sound ∝ = \(\frac{1}{\sqrt{\text { Density of gas }}}\)

(b) Effect of humidity: Sound travels faster in moist air than in dry air.

(c) Effect of temperature: The speed of sound in a gas is directly proportional to the square root of its absolute temperature.
Speed of sound ∝= \(\sqrt{\text { Absolute temperature of gas }}\)
So, the speed of sound increases with the increase in temperature of the gas. For example, the speed of sound in air is 331 ms-1 at 0°C and 344 ms-1 at 20°C.

(d) Effect of wind: Sound is carried by air, so the speed of sound increases when the wind blows in the direction of sound and speed of sound decreases when the wind blows in the direction opposite to the direction of sound.

JAC Class 9 Science Important Questions Chapter 12 Sound

Question 2.
Explain some important applications of ultrasound in industry and medicine.
Answer:
Applications of ultrasound in industry and medicine are as follows:

  • Industrial applications:
    1. The construction of big structures like buildings, bridges, machines, scientific equipment, etc., use metallic components.
    2. The cracks or holes inside the block reduce the strength of the structure. Such defects are not visible from outside. Ultrasonic waves can be used to detect such defects.
    3. Ultrasonic waves are allowed to pass through the metal block and detectors are used to detect the transmitted waves. If there is even a small defect, the ultrasound gets reflected back and does not reach the detector. This is how the presence of a flaw or defect is detected.
  • Medical applications:
  1. Echocardiography: In this technique, ultrasonic waves are made to reflect from various parts of the heart to form the image of the heart.
  2. Ultrasonography: Ultrasonic waves can be used to develop three dimensional photographs of different parts of the human body. This technique is called ultrasonography.
    • This technique is also used to monitor the growth of a foetus inside its mother’s womb In this technique, the ultrasonic waves travel through the tissues of the body and get reflected from a region where there is a change of tissue density.
    • These waves are then converted into electrical signals that are used to generate images of the organ. These images are then displayed on a monitor or printed on a film.
  3. In surgery: Ultrasonic waves are commonly used in cataract removal. Ultrasonic waves are also used to grind small stones formed in the kidneys. These grinded grains are flushed with urine.

Question 3.
State some important characteristics of wave motion.
Answer:
Characteristics of wave motion are as follows:

  1. It is the disturbance which travels forward through the medium and not the particles of the medium. The particles of the medium merely vibrate about their mean positions.
  2. Each particle receives vibrations a little later than its preceding particle.
  3. The velocity with which wave travels is different from the velocity of the particles with which they vibrate about their mean positions.
  4. The wave velocity remains constant in a given medium while the particle velocity changes continuously during its vibration about the mean position.

Question 4.
How can a longitudinal wave be represented graphically?
Answer:
Graphical representation of a longitudinal wave:
JAC Class 9th Science Solutions Chapter 12 Sound 6
Sound propagates as density or pressure variations as shown in (a), (b) and (c).

  1. When a longitudinal wave passes through a medium, the particles of the medium come closer together and move away from one another alternately. Thus, alternate regions of increased and decreased density are created. These regions are called compressions and rarefactions respectively.
  2. The figures (a) and (b) represent the density and pressure variations, respectively, as the sound wave propagates through a medium.
    Figure (c) represents the variations of density and pressure graphically.
  3. The variation of density increases or decreases as the pressure of the medium at a given time increases or decreases with distance, above and below the average value of density and pressure.
  4. The distance between two successive compressions (C) or two successive rarefactions (R) is called wavelength. It is usually represented by λ (lambda).

Question 5.
Explain the formation of waves with the help of an example.
Answer:
A wave is a pattern of disturbance which travels through a medium due to repeated vibrations of the particles of the medium, the disturbance being handed over from one particle to the next. The motion of the disturbance is called wave motion. If we drop a pebble into a pond of still water, a circular pattern of alternate crests and troughs spreads out from the point where the pebble strikes the water surface. The kinetic energy of the pebble makes the particles which come in contact with it oscillate.

These particles, in turn, transfer energy to the particles of next layer which begin to oscillate. Energy is further transferred to the particles of the next layer which also begin to oscillate and so on. In this way, energy is carried by the waves from one part to another. Further, if we throw pieces of paper or a cork on the water surface, it will oscillate up and down about its mean position and will not move forward with the wave. This shows that it is the disturbance of the wave which travels forward and not the particles of the medium.

Question 6.
A ship sends out ultrasound that returns from the seabed and is detected after 4 s. If the speed of ultrasound through seawater is 1550 m/s, what is the distance of the seabed from the ship?
Answer:
Time between transmission and detection, t = 4s
Speed of ultrasound in sea water,
v = 1550 m/s
Distance travelled by the ultrasound
= 2 × depth of the sea = 2d
where d is the depth of the sea.
2d = Speed of sound × time = 1550 m/s × 4s = 6200m
d =\(\frac{6200}{2}\) m = 3100 m = 3.1 km.
Thus, the distance of the seabed from the ship is 3100 m or 3.1 km.

Analysing & Evaluating Questions

Question 7.
A sound were travelling in a medium is represented as shown in the figure
JAC Class 9th Science Solutions Chapter 12 Sound 7
(a) Which letter represents the amplitude of the sound wave?
(b) Which letter represents the wavelength of wave?
(c) What is the frequency of the source of sound if the vibrating source of sound makes 360 oscillations in 2 minutes?
Answer:
In the figure,
(a) The amplitude is represented by X.
(b) The wavelength is represented by Y.
(c) Frequency
= \(\frac{No. of oscillations }{ Time in sec onds}\) = \(\frac{360}{2 \mathrm{~min}}\)
= \(\frac{360}{2 \times 60 \mathrm{~s}}\) = 3s-1 = Hz

Activity-1

  • Take a tuning fork and set it vibrating by striking its prong on a rubber pad. Bring it near your ear and observe.
  • Touch one of the prongs of the vibrating tuning fork with your finger and see what happens.
  • Take a table tennis ball or a small plastic ball Now,Take a big needle and a thread, put a knot at one end of the thread, and then with the help of the needle, pass the thread through the ball. Suspend the ball from a support. Now, touch the ball gently with the prong of a vibrating tuning fork. Observe what happens.
    JAC Class 9th Science Solutions Chapter 12 Sound 8

Observations

  • A sound is heard on bringing the vibrating fork near the ear.
  • If we touch the ball with a turning fork set into vibration, the ball gets displaced from its mean position and starts oscillating.

Activity 2

  • Fill water in a beaker or a glass up to the brim. Gently touch the water surface with one of the prongs of the vibrating tuning fork, as shown in the figure.
  • Next, dip the prongs of the vibrating tuning fork in water, as shown in the figure.
  • Observe what happens in both the cases.
    JAC Class 9th Science Solutions Chapter 12 Sound 9

Observations
In both the cases, sound will be produced by the turning fork which produces ripples in water. But in case (1), ripples are produced which will move up and down and in case (2), ripples are produced which will move sideways.

Activity 3

  • Take a spring. Ask your friend to hold one of its end. You hold the other end. Now stretch the slinky as shown in the figure. Then give it a sharp push towards your friend and observe.
  • Move your hand pushing and pulling the slinky alternatively and observe again.
    JAC Class 9th Science Solutions Chapter 12 Sound 10

Observations

  • When we give a small jerk, a hump is produced and this travels forward. It represents a transverse wave.
  • When we give a sharp push, a continuous disturbance is produced. This disturbance starts moving in the forward and backward direction parallel to the direction of propagation of the disturbance. It represents a longitudinal wave.
  • If you mark a dot on the slinky, you will observe that the dot on the slinky will move back and forth parallel to the direction of the propagation of the disturbance.

Activity 4

  • Take two identical pipes, as shown in the figure. You can make pipes using a chart paper. The length of the pipes should be sufficiently long as shown.
  • Arrange them on a table near a wall.
  • Keep a clock near the open end of one of the pipes and try to hear the sound of the clock through the other pipe.
  • Adjust the position of the pipes, so that you can hear the best sound of the clock.
  • Now, measure the angles of incidence and reflection and see the relationship between the angles.
  • Lift the pipe on the right, vertically to a small height and observe what happens.
    JAC Class 9th Science Solutions Chapter 12 Sound 11

Observations

  • Reflection of sound is similar to the reflection of light, i.e., angle of incidence = angle of reflection.
  • If we lift the pipe vertically to a small height, we will not be able to hear the sound through the other end of the pipe because the incident sound wave, the reflected sound wave and the normal, all he in the same plane.

Value Based Questions

Question 1.
Sahil noticed that his pet dog was frightened and trying to hide in a safe place in his house when some crackers were burst in the neighbourhood. He realised the problem and he decided not to burst crackers during diwali or for any other celebrations.
1. What must be the range of sound of crackers?
2. Name two diseases that can be caused due to noise pollution.
3. Name the values of Sahil reflected in the above act.
Answer:

  1. The range of crackers sound must be between 20 Hz and 20 kHz.
  2. Two diseases that can occur due to noise pollution are heart attack and high blood pressure.
  3. Sahil reflects the value of respect and sensitivity for animals and caring for animals.

Question 2.
It is not advisable to construct houses near airports. Inspite of that, many new apartments are constructed near airports. Rahul files RTI and also complains to the municipal office about the same?
1. Why should we not reside near airport?
2. Name two other places where there is noise pollution.
3. What value of Rahul is reflected in this act?
Answer:

  1. The landing and taking off of the airplanes cause a lot of noise pollution which may lead to deafness, high blood pressure, and other health problems.
  2. The other two places where there is noise pollution are heavy traffic routes and railway stations or lines.
  3. Rahul shows the values of a responsible citizen and shows awareness.

JAC Class 9 Science Important Questions

JAC Class 9 Science Important Questions Chapter 11 Work and Energy

JAC Board Class 9th Science Important Questions Chapter 11 Work and Energy

Multiple Choice Questions

Question 1.
The gravitational potential energy of an object is due to
(a) it’s mass
(b) its acceleration due to gravity
(c) its height above the earth’s surface
(d) all of the above
Answer:
(d) all of the above

Question 2.
The unit of work is the joule. The other physical quantity that has the same unit is
(a) power
(b) velocity
(c) energy
(d) force
Answer:
(c) energy

Question 3.
If the velocity of a body is doubled, its kinetic energy
(a) gets doubled
(b) becomes half
(c) does not change
(d) becomes 4 times
Answer:
(d) becomes 4 times

Question 4.
A student carries a bag weighing 5 kg from the ground floor to his class on the first floor that is 2 m high. The work done by the boy is
(a) 1J
(b) 10J
(c) 100J
(d) 1000J
Answer:
(c) 100J

Question 5.
How much time will be required to perform 520 J of work at the rate of 20 W?
(a) 24s
(b) 16s
(c) 20s
(d) 26s
Answer:
(d) 26s

Question 6.
A body of mass 2 kg is dropped from a height of lm. Its kinetic energy as it touches the ground is
(a) 19.6N
(b) 19.6J
(c) 9.8m
(d) 9.8J
Answer:
(b) 19.6J

JAC Class 9 Science Important Questions Chapter 11 Work and Energy

Question 7.
The unit of power is
(a) watt per second
(b) joule
(c) kilojoule
(d) joule per second
Answer:
(d) joule per second

Question 8.
A coolie carries a load of 500 N to a distance of 100 m. The work done by him is
(a) 5 Nm
(b) 50,000 Nm
(c) 0 Nm
(d) 1/5 N m
Answer:
(c) 0 Nm

Question 9.
Power is a measure of the
(a) rate of change of momentum
(b) force which produces motion
(c) change of energy
(d) rate of change of energy
Answer:
(d) rate of change of energy

Question 10.
If the speed of an object is doubled, its kinetic energy is
(a) doubled
(b) quadrupled
(c) halved
(d) tripled
Answer:
(b) quadrupled

Question 11.
Which of the following is not correct?
(a) Energy is the ability of doing work
(b) Work can be expressed as F × s
(c) Unit of power is joule
(d) Power is the amount of work done per unit of time
Answer:
(d) Power is the amount of work done per unit of time

Question 12.
kW h is the unit of
(a) acceleration
(b) work
(c) power
(d) energy
Answer:
(c) power

Question 13.
Considering air resistance negligible, the sum of potential and kinetic energies of a free falling body would be
(a) zero
(b) increasing
(c) decreasing
(d) fixed
Answer:
(d) fixed

Question 14.
Two bodies of masses m] and m2 have equal kinetic energies. If P1 and P2 are their respective momenta, the ratio of P1 to P2 is
(a) m1 : m2
(b) m2 : m1
(c) \(\sqrt{\mathrm{m}_{1}} : \sqrt{\mathrm{m}_{2}}\)
(d) \(m_{1}^{2} : m_{2}^{2}\)
Answer:
(c) \(\sqrt{\mathrm{m}_{1}} : \sqrt{\mathrm{m}_{2}}\)

Question 15.
A light and a heavy body have equal momenta Which one has greater kinetic energy?
(a) The lighter body
(b) The heavier body
(c) Both have same KE
(d) None of these
Answer:
(b) The heavier body

Analysing & Evaluating Questions

Question 16.
A car is accelerated on a levelled road and attains a velocity four times of its initial velocity. In this process the potential energy of the car
(a) does not change
(b) becomes twice to that of initial
(c) becomes 4 times that of intial
(d) becomes 16 times that of initial
Answer:
(a) does not change

Question 17.
An iron sphere of mass 10 kg has the same diameter as an aluminium sphere of mass 3.5 kg. Both spheres are dropped simultaneously from a tower. When they are 10 m above the ground, they have the same
(a) acceleration
(b) momenta
(c) potential energy
(d) kinetic energy
Answer:
(a) acceleration

Question 18.
A girl is carrying a school bag of 3 kg mass on her back and moves 200 m on a levelled road. The work done against the gravitational force will be (g = 10 m-2)
(a) 6 × 103J
(b) 6J
(c) 0.6J
(d) zero
Answer:
(d) zero

Assertion Reason Questions

Directions: In the following questions, the Assertions and the Reasons have been put forward. Read the statements carefully and choose the correct alternative from the following:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.
(C) The assertion is true but the reason is false.
(D) Both the statements are false.
1. Assertion: Work, the product of force and displacement, is a vector quantity.
Reason: Product of two vector quantities is always a vector quantity.
Answer:
(D) Both the statements are false.

2. Assertion: When a book is moved from a table to the top of an almirah, its potential energy increases.
Reason: Higher the height of a body from the ground level, higher is its potential energy.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

3. Assertion: A person carrying a suitcase on his head is not doing any work. Reason: The force applied by the person is acting in the downward direction.
Answer:
(C) The assertion is true but the reason is false.

4. Assertion: The work done by the force of gravity on the moon revolving around the earth is zero.
Reason: The gravitational force and the displacement of moon are at right angles to each other.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

5. Assertion: Work done on an object can be positive, negative or zero.
Reason: Work done is a scalar quantity.
Answer:
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.

Very Short Answer Type Questions

Question 1.
Define work.
Answer:
Work is said to be done when a force applied on a body produces a displacement of the body. It is given by W = F x s where ‘F’ is the force applied and ‘s’ is the displacement caused.

Question 2.
State reason why work is a scalar quantity.
Answer:
Work is the product of force (F) and displacement (s). Since both F and s are vector quantities and the dot product of vector quantities produces a scalar quantity, therefore, work is a scalar quantity.

JAC Class 9 Science Important Questions Chapter 11 Work and Energy

Question 3.
Name two kinds of potential energies.
Answer:
Gravitational potential energy and elastic potential energy.

Question 4.
If the work done is 20J and displacement is 2m, find the force applied.
Answer:
Given, W = 20J and s = 2m.
W = F × s
20 = F × 2
F= 10 N

Question 5.
Name the energy stored in a rubber band when it is stretched?
Answer:
On stretching a rubber band, potential energy is stored in it.

Question 6.
State the law of conservation of energy.
Answer:
It states that energy can neither be created nor destroyed. It can only change its form.

Question 7.
When a book is lifted from a table, against which force is the work done?
Answer:
Work is done against the force of gravity.

Question 8.
Define the commercial unit of energy.
Answer:
The commercial unit of energy is kW h (kilowatt hour). 1 kW h is the energy used in one hour at the rate of 1000 J per second.
1 kWh = 1 kW × 1 h = 3.6 × 106j

Question 9.
A light and a heavy body have equal kinetic energies. Which one is moving faster?
Answer:
The lighter body is moving faster because for the same kinetic energy, velocity is inversely proportional to the mass.
Analysing & Evaluating Question uestions

Question 10.
Two objects of same mass are placed at positions A and B as shown in the figure. Both of them are raised to the position C. In which case, the potential energy is more?
Answer:
The object at A will gain more potential energy than the object at B. But the final potential energy of both A and B will be equal when raised to position C.

Question 11.
A rocket is moving up with a velocity v. If the velocity of this rocket is suddenly tripled, what will be the ratio of the itwo kinetic energies?
Answer:
K.E. °c (velocity)2
When the velocity is tripled, K.E. increases by a factor of 9 ( = 32)
Thus, the ratio of the two kinetic energies is 1 : 9.

Question 12.
Can any object have momentum even if its mechanical energy is zero? Explain.
Answer:
No. Zero mechanical energy means no potential energy and no kinetic energy. Zero kinetic energy means, zero velocity. As a result, momentum is also zero (as P = mv).

Short Answer Type Questions

Question 1.
Calculate the work done by a man in rotating a wheel of an amusement slide in a fair 40 times in 1 minute?
Answer:
The man is rotating the wheel of an amusement slide by just standing at a place. This concludes that the wheel is not undergoing any displacement. Since displacement is zero, therefore, work done is zero.

Question 2.
Define positive work done and negative work done.
Answer:

  1. Positive work (done: Work done is positive when the displacement occurs in the direction of force.
  2. Negative work done: Work done is negative when the displacement occurs opposite to the direction of force.

Question 3.
In which of the following cases, work is said to be done?
1. When we push a table and the table is displaced.
2. When a person holds a book in his hand and keeps it stationary.
3. When a wire is twisted.
JAC Class 9th Science Solutions Chapter 11 Work and Energy 4
Answer:

  1. When we push a table and the force applied by us is large enough to move it from its original position, then work is said to be done.
  2. When a person holds a book in his hand and keeps it stationary, there occurs no movement of the book. In this case, though a force is constantly being applied, there is no displacement and hence work done is zero.
  3. When a wire is twisted, the shape of the wire changes which concludes that work is done as there occurred changes in the configuration of the wire.

Question 4.
What will be the nature of work done when the force acting on a body retards its motion? Justify your answer by quoting examples.
Answer:
When force retards the motion of a body, the motion is stopped, i.e., a force opposite to the direction of the motion is applied. Thus, a negative work is done by the force.
For example:

  1. In tug of war, the work done by the losing team is negative.
  2. When a ball is thrown up in the air, the gravitational force acting downwards upon the ball does negative work on the ball.

Question 5.
What is gravitational potential energy?
Answer:
The gravitational potential energy of an object at a point above the ground
is defined as the work done in raising an object from the ground to that point against gravity.
GPE = mgh

JAC Class 9 Science Important Questions Chapter 11 Work and Energy

Question 6.
Differentiate between potential energy and kinetic energy.
Answer:

Potential Energy Kinetic Energy
(a) Energy possessed by a body due to its position, shape or configuration. (a) Energy possessed by a body due to its motion.
(b) P.E. = mgh where, m = mass, g = acceleration due to gravity, h = height. (b) K.E. = \(\frac{1}{2}\) mv2 where, m = mass, v = velocity.

Question 7.
State two situations where energy is supplied but no work is done.
Answer:
(a) A person pushing a heavy rock is using all the energy but if the rock does not move, no work is done, (b) A person standing with heavy load on his head is spending energy in doing this, but no work is done.

Question 8.
How are work and energy related to each other?
Answer:
An object having a capability to do work is said to possess energy. The object which does work loses energy and the object on which work is done, gains energy. The unit of both energy and work is joule.

Question 9.
On what factor does the gravitational potential energy depend?
Answer:
Gravitational potential energy depends on the height of object from the ground level zero level we choose. Example: A ball tossed from the second floor of a building will attain a height, say h, from its roof, but from the first floor its height will be h ‘where h > h’.
Hence, the potential energy of the ball on the first floor level is less as compared to that on the second floor.

Question 10.
Write the form of energy possessed by the body in the following situations:
(a) A coconut falling from tree
(b) An object raised to a certain height
(c) Blowing wind
(d) A child driving a bicycle on the road
Answer:
(a) Kinetic energy + Potential energy
(b) Potential energy
(c) Kinetic energy
(d) Kinetic energy

Question 11.
What is energy? Give the unit of energy. Name the different forms of energy.
Answer:
Energy of a body is defined as its capacity or ability to do work. When a body is capable of doing more work, it is said to possess more energy.
The SI unit of energy is joule (J).
Energy has many forms: potential energy, kinetic energy, heat energy, chemical energy, electrical energy, light energy, solar energy, etc.

Question 12.
Derive an equation for kinetic energy of an object?
Answer:
The kinetic energy of a body can be determined by calculating the amount of work required to set the body into motion with the velocity ‘v’ from its state of rest. Suppose,
m = mass of the body
u = 0 = initial velocity of the body
F = force applied on the body
a = acceleration produced in the body in
the direction of force
v = final velocity of the body
s = distance covered by the body
As v2 – u2 = 2as
= v2 – 02 = 2as
a= \(\frac{v^{2}}{2 s}\)
As the force and displacement are in the same direction, the work done on the body is
W = Fs = mas = m \( \frac{\mathrm{v}^{2}}{2 \mathrm{~s}}\)s = \(\frac{1}{2}\) mv2
This work done appears as the kinetic energy of the body.
∴ KE = \(\frac{1}{2}\) mv2

Question 13.
Derive an equation for potential energy?
Answer:
Let the work done on the object against gravity be W.
Work done, W = force × displacement
Work done, W = mg × h
Work done, W = mgh
Since work done on the object is equal to mgh, an energy equal to mgh units is gained by the object. This is the potential energy (Ep) of the object.
Ep = mgh

Question 14.
An electric heater of 1000 W is used for 2 hours a day. What is the cost of using it for a month of 28 days, if 1 unit costs ₹ 3.00?
Answer:
Here, P = 1000W = lkW
Total time, t = 2 × 28 hours = 56 hours
Total energy consumed = P × t
= 1 kW × 56 h = 56 kW h
Cost of 1 kWh = ₹ 3.00
Cost of 56 kWh = 3 × 56 = ₹ 168.

Analysing & Evaluating Questions

Question 15.
Two identical pointed objects made from iron and wood are allowed to fall on a heap of sand from the same height. The iron object penetrates more in sand than the wooden object. Which of the objects has more potential energy?
Answer:
Of the two identical objects, the one made from iron will have greater mass. So when it falls from a height, it will possess greater kinetic energy as compared to the wooden object. As a result,
(a) the iron object will penetrate more in sand.
(b) the iron object will have more potential energy.

Question 16.
The weight of a person on a planet A is about half that on the earth. He can jump upto 0.4 m height on the surface of the earth. How high can he jump on the planet A?
Answer:
The weight of a person on planet A is about half that on the earth. This means, the acceleration due to gravity of the planet A is half that of the earth. So, Height of the jump on the surface of planet A = \(\frac{0.4 \mathrm{~m}}{1 / 2}\) = 0.8 m

Long Answer Type Questions

Question 1.
How is work done measured when a body moves in a direction inclined to the direction of the applied force?
Answer:
In the figure, a force F pulls a block making angle 0 with the horizontal surface. Under this force, suppose the block moves from position A to B after covering a distance ‘s’.
JAC Class 9th Science Solutions Chapter 11 Work and Energy 5
Let, F1 = Component of force in the direction of displacement ‘s’
Then, \(\frac{F_{1}}{F}\) = cos θ or F1 = F cos θ
Work done = Component of force in the direction of displacement × displacement
W = F1 × s = F cos θ x s
W = Fs cos θ
Special cases:
(a) When θ = 0°,
cos θ = 1 and W = Fs
Thus, work done is maximum when the displacement of the body is along the direction of the force.

(b) When θ = 90°,
cos θ = 0 and W = 0
Thus, work done is zero when the displacement of the body is perpendicular to the direction of force.

(c) When θ = 180°,
cos θ = -1 and W = – Fs
Thus, work done is negative when displacement is opposite to the direction of force.

(d) When s = 0, W = 0 Thus, work done on a stationary body is zero.

JAC Class 9 Science Important Questions Chapter 11 Work and Energy

Question 2.
What is meant by potential energy of a body? Give some examples.
Answer:
The energy possessed by a body by the virtue of its position, shape or configuration is called its potential energy.

  1. Examples of P.E. due to position:
    • Water stored in a dam at a height has potential energy.
    • A stone lying on the roof of the building has potential energy.
  2. Examples of P.E. due to shape:
    • In a toy car, the wound spring possesses potential energy. As the spring is released, its potential energy changes into kinetic energy which moves the toy car.
    • Energy possessed by a stretched rubber band is potential energy.
  3. Example of P.E. due to configuration:
    • A stretched bow possesses potential energy. As soon as it is released, it shoots the arrow in the forward direction with a large velocity.
    • The potential energy of the stretched bow gets converted into the kinetic energy of the arrow.
      JAC Class 9th Science Solutions Chapter 11 Work and Energy 6

Question 3.
A 100 W electric bulb is lighted for 2 hours every day and five 40 W tubes are lighted for 4 hours every day. Calculate:
(a) the energy consumed for 60 days and
(b) the cost of electricity consumed at the rate of ₹3 per kW h.
Answer:
(a) Energy consumed by a 100 W bulb each day = 100 W × 2 h
= 200 Wh = \(\frac{200}{1000}\)= 0.2 kW h
Energy consumed by five 40 W tubes each day = 5 × 40 W × 4h
= 800 Wh = \(\frac{800}{1000}\) = 0.8 kW h
Total energy consumed each day = 0.2 + 0.8 = 1.0 kWh
Total energy consumed in 60 days = 1.0 x 60 = 60 kWh

(b) Cost of 1 kW h = ₹ 3
Cost of 60 kW h = 3 × 60 = 180

Question 4.
Answer the following:
(a) List any three situations in your daily life where you can say that work has been done.
(b) How much work is done in increasing the velocity of a car from 15 km/h to 30 km/h if the mass of the car is 1000 kg?
Answer:
(a) Three situations where work is done are:

  1. Pushing a pebble lying on the ground. The pebble moves through some distance. Here, we apply a force and the pebble gets displaced. So, we have done work on the pebble.
  2. We apply a force to lift a book through a height. The book rises up. We have done work in moving up the book.
  3. A bullock is pulling a cart and the cart moves. There is a force on the cart and the cart has moved. The bullock has done work on the cart.

JAC Class 9th Science Solutions Chapter 11 Work and Energy 7
(b) According to the question,
u = 15 km/h = 4 m/s
v = 30 km/h = 8 m/s
Mass = 1000 kg
W = ?
W = K.E. = \(\frac{1}{2}\) m(v2 – u2)
\(\frac{1}{2}\) × 1000 × ((8)2 – (4)2)
= \(\frac{1}{2}\) × 1000 × (64 – 16)
= \(\frac{1}{2}\) × 1000 × (675) = 24,000J
Hence, work done is 24,000J.

Analysing & Evaluating Questions

Question 5.
A boy is moving on a straight road against a frictional force of 5N. After traveling a distance of 1.5 km he forgot the correct path at a roundabout of radius 100 m. However, he moves on that circular path for one and half cycle and then he moves forward up to 2.0 km. Calculate the work done by him.
Answer:
Work done by the boy while moving on a straight road
W = F × s
W = 5N × 1.5 km
= 5 kg m s-2 × 1500 m = 7500J
Work done during moving around circular path
= 5N × (2 × 100 m) = 1000J
Work done during moving further by
2.0 km = 5N × (2 × 1000 m) = 10,000J
Total work done by the boy = 7500J + 1000J + 10,000J
= 18500J

Activity 1

  • Take a heavy ball. Drop it on a thick bed of sand. A wet bed of sand would be better. Drop the ball on the sand bed from a height of about 25 cm and observe the results.
  • Repeat this activity from heights of 50 cm, lm and 1.5 m.
  • Ensure that all the depressions are distinctly visible.
  • Mark the depressions to indicate the height from which the ball was dropped.
  • Compare their depths.

Observations

  • The ball that falls from the height of 1.5 m creates the deepest depression.
  • The ball that falls from the height of 50 cm creates the shallowest depression.
  • Larger the height from which the ball is dropped, larger is the kinetic energy gained by the ball on reaching the ground and more is its capability of doing work.

Activity 2

  1. Set up the apparatus as shown in the figure.
  2. Place a wooden block of known mass in front of the trolley at a convenient fixed distance.
  3. Place a known mass on the pan so that the trolley starts moving.
  4. The trolley moves forward and hits the wooden block.
  5. Fix a stop on the table in such a manner that the trolley stops after hitting the block. The block gets displaced.
  6. Note down the displacement of the block.
  7. Repeat this activity by increasing the mass on the pan. Observe, in which case is the displacement more.
    JAC Class 9th Science Solutions Chapter 11 Work and Energy 8

Observations

  1. The force of gravity pulls the mass in the pan in the downward direction. This force gets transferred to the trolley through the string.
  2. The trolley moves and hits the block with a force.
  3. The larger the mass in the pan, the larger is the force with which the trolley hits the block.
  4. Consequently, larger will be the displacement and larger will be the work done. The moving trolley possess energy and hence does work on the block.

Activity 3

  • Take a slinky as shown below.
  • Ask a friend to hold one of its ends. You hold the other end and move away from your friend. Now, you release the slinky and observe.
    JAC Class 9th Science Solutions Chapter 11 Work and Energy 9

Observations

  • When released, the slinky regains its original length. The slinky has acquired potential energy due to the work done on it during stretching. On releasing, potential energy is converted into kinetic energy.
  • The slinky will also acquire energy when it is compressed.

Value Based Questions

Question 1.
Apoorva saw few planter pots kept on the balcony sill of fourth floor in her building. She makes an effort and keeps all the planter pots down the sill.
1. What type of energy is present in the pot kept on the balcony sill of fourth floor?
2. If the pot falls from the fourth floor, what type of energy will be seen in the falling pot?
3. What value of Apoorva is reflected in the above act?
Answer:
1. The pot on the sill possesses potential energy.
2. The falling pot possesses both the kinetic energy and the potential energy.
3. Apporva showed the value of moral responsibility and awareness.

Question 2.
Siddharth saw a lady labourer who carried bricks on her head from one point of the construction site to the other end which was some 500 m away. He prepares a trolley for the labourer to carry the bricks to make her work easier.
1. In carrying the bricks from point A to point B on the head by the lady labourer in the construction site, is any work done by the labourer?
2. By pulling the trolley of bricks from point A to point B, is any work done?
3. What value of Siddharth is seen in the above act?
Answer:
1. In carrying the bricks from point A to point B on head by the lady, no work is said to be done.
2. By pulling the trolley of bricks, work is said to be done.
3. Siddharth showed kindness, general awareness and sympathy.

JAC Class 9 Science Important Questions

JAC Class 9 Science Important Questions Chapter 10 Gravitation

JAC Board Class 9th Science Important Questions Chapter 10 Gravitation

Multiple Choice Questions 

Question 1.
The mass of a body on moon is 40 kg. What is its weight on the earth?
(a) 240 kg
(b) 392 N
(c) 240 N
(c) 400 kg
Answer:
(b) 392 N

Question 2.
The gravitational force between two objects is
(a) attractive at large distance only
(b) attractive at small distance only
(c) attractive at all distances
(d) attractive at large distance but repulsive at small distance
Answer:
(c) attractive at all distances

Question 3.
A body of mass 1 kg is attracted by the earth with a force equal to
(a) 9.8 N
(b) 1 N
(c) 6.67 × 1011 N
(d) 9.8 m/s
Answer:
(a) 9.8 N

Question 4.
The earth attracts a body with a force of 10 N. With what force does that the body attract the earth?
(a) 10N
(b) 1 N
(c) \(\frac{1}{10 \mathrm{~N}}\)
(d) 2 N
Answer:
(a) 10N

Question 5.
The SI unit of G is
(a) Nm2 kg-1
(b) Nm2 kg-2
(c) Nm2 kg
(d) N-1 m2 kg-2
Answer:
(b) Nm2 kg-2

JAC Class 9 Science Important Questions Chapter 10 Gravitation

Question 6.
The gravitational force of attraction between two bodies of 1 kg each and 1 m apart is
(a) 6.67 × 10-11 N
(b) 6.67 × 10-8 N
(c) 6.67 × 1011 N
(d) 6.67 × 108 N
Answer:
(a) 6.67 × 10-11 N

Question 7.
The value of acceleration due to gravity near the earth’s surface is
(a) 8.9 m-2
(b) 9.8 ms-2
(c) 8.9 cms-2
(d) 9.8 cms-2
Answer:
(b) 9.8 ms-2

Question 8.
Consider an elevator moving downwards with an acceleration a The force exerted by a passenger of mass m on the floor of the elevator is
(a) ma
(b) ma – mg
(c) mg – ma
(d) mg + ma
Answer:
(c) mg – ma

Question 9.
If the earth suddenly shrinks to half of its present size, the value of acceleration due to gravity will
(a) become twice
(b) remain unchanged
(c) become half
(d) become four times
Answer:
(d) become four times

Question 10.
The weight of a body would not be zero
(a) at the centre of the earth
(b) during a free fall of an elevator
(c) in interplanetary space
(d) on a frictionless surface
Answer:
(d) on a frictionless surface

Question 11.
Newton’s law of gravitation
(a) can be verified in a laboratory
(b) cannot be verified but is true
(c) is valid only on earth
(d) is valid only in the solar system
Answer:
(a) can be verified in a laboratory

Question 12.
10 kg weight is equal to
(a) 9.8 N
(b) 98 N
(c) 980 N
(d) \(\frac{1}{9.8}\) N
Answer:
(b) 98 N

Question 13.
The weight of a body cannot be expressed in
(a) kg wt
(b) N
(c) dyne
(d) kg
Answer:
(d) kg

Question 14.
A stone is dropped from a cliff. Its speed after it has fallen 100m is
(a) 9.8 m/s
(b) 44.2 m/s
(c) 19.8 m/s
(d) 98 m/s
Answer:
(b) 44.2 m/s

Question 15.
At which of the following locations, the value of g is the largest?
(a) On top of the Mount Everest
(b) On top of Qutub Minar
(c) At a place on the equator
(d) A camp site in Antarctica
Answer:
(d) A camp site in Antarctica

Analysing & Evaluating Questions

Question 16.
An apple falls from a tree because of gravitational attraction between the earth and apple. If Ft is the magnitude of force exerted by the earth on the apple and F2 is the magnitude of force exerted by the apple on the earth, then
(a) F1 is very much greater than F2
(b) F2 is very much greater than F1
(c) F1 is only a little greater than F2
(d) F1 and F2 are equal
Answer:
(d) F1 and F2 are equal

Question 17.
An object is put one by one in three liquids having differei dnsities. The object floats with\(\frac{1}{9}\), \(\frac{2}{11}\) and \(\frac{3}{7}\) part of its volume outside dit liquid surface in liquids of densities d1, d2 and d3 respectively. Which of the following is correct?
(a) d1 > d2 > d3
(b) d1 >d2 <d3
(c) d1 < d2 > d3
(d) d1 < d2 < d3
Answer:
(d) d1 < d2 < d3

Question 18.
An object weighs 10N in air. When immersed fully in water, it weighs only 8N. The weight of the liquid displaced by the object will be
(a) 2 N
(b) 8 N
(c) 10 N
(d) 12
Answer:
(a) 2 N

Assertion Reason Questions

Directions: In the following questions, the Assertions and the Reasons have been put forward. Read the statements carefully and choose the correct alternative from the following:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.
(C) The assertion is true but the reason is false.
(D) Both the statements are false.
1. Assertion: The law of gravitation is not applicable on the two bodies lying on the surface of the earth.
Reason: Law of gravitation is applied to celestial bodies only.
Answer:
(D) Both the statements are false.

2. Assertion: Mass of a body remains same at all the places.
Reason: Mass of a body is independent of acceleration due to gravity.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

3. Assertion: Value of acceleration due to gravity is greater at the poles than at the equator.
Reason: Distance between pole and the centre of the earth is less than the distance between the equator and the centre of the earth.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

4. Assertion: One can jump higher on the surface of the moon than on the earth. Reason: The value of g (acceleration due to gravity) on the moon is greater than that on the earth.
Answer:
(C) The assertion is true but the reason is false.

5. Assertion: Fluids exert an upthrust on the objects immersed in them.
Reason: The upthrust is equal to the weight of the liquid displaced.
Answer:
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.

Very Short Answer Type Questions

Question 1.
Define the term ‘gravitation’.
Answer:
Every object in this universe attracts every other object with a force known as ‘force of gravitation’. Gravitation is the force of attraction between any two bodies in the universe.

Question 2.
Give the SI unit and value of G.
Answer:
SI unit of G = \(\frac{\mathrm{Nm}^{2}}{\mathrm{~kg} \cdot \mathrm{kg}}\) = N m2 kg-2
Its value = 6.67 × 10-11 N m2 kg-2.

Question 3.
g = GM/R2, what do the symbols in this formula denote?
Answer:
g = Acceleration due to gravity
G = Gravitational constant
M = Mass of the earth
R = Radius of the earth

Question 4.
Name the scientist who first determined the value of G experimentally.
Answer:
Henry Cavendish first determined the value of G experimentally, in the year 1778, using a sensitive balance.

JAC Class 9 Science Important Questions Chapter 10 Gravitation

Question 5.
Why is G called a universal gravitational constant’?
Answer:
The value of constant G is same for any pair of objects in the universe. Also, its value does not depend on the nature of the intervening medium. That is why constant G is called ‘universal’, whether the bodies are big or small, or whether they are celestial or terrestrial.

Question 6.
State any two properties of gravitational force.
Answer:

  1. It is always attractive in nature.
  2. It does not depend on the nature of the medium between the two bodies.

Question 7.
Which force is responsible for the stability of our universe?
Answer:
The force of gravitation.

Question 8.
How is ‘g’ on the surface of the earth related to ‘G’?
Answer:
g = \(\frac{\mathrm{GM}}{\mathrm{R}^{2}}\) = \(\frac{1.67 \times\left(1.74 \times 10^{6}\right)^{2}}{6.67 \times 10^{-11}}\)

where M = mass of the earth,
R = radius of the earth.

Question 9.
How is weight of an object related to its mass?
Answer:
Weight (w) = mass (m) × acceleration due to gravity (g).

Question 10.
What is the SI unit of pressure?
Answer:
The SI unit of pressure = N/m2 = Pascal.

Question 11.
Define thrust. What is the SI unit of thrust?
Answer:
The net force exerted by a body in a particular direction is called thrust. The SI unit of thrust is newton.

Question 12.
Why does a truck or a motorbike have much wider tyres?
Answer:
A truck or a motorbike has much wider types so that the pressure exerted by it can be distributed to more surface area of the road and avoid the wear and tear of tyres.

Question 13.
In what sense does the moon fall towards the earth? Why does it not actually fall on the earth’s surface?
Answer:
At each point of its orbit, the moon falls towards the earth instead of going straight. It does not fall on the earth because it is moving in a circular orbit. The moon is kept in its circular orbit by the centripetal force provided by the force of attraction of the earth.

Question 14.
The earth attracts an apple from the tree and it falls but the earth does not appear to move towards the apple. Why?
Answer:
The mass of the earth is extremely large as compared to that of the apple. So the acceleration produced is very small as compared to that in the apple. Hence, the motion of the earth towards the apple is not noticeable.

Question 15.
What do you mean by the term ‘free fall’?
Answer:
The motion of a body under the influence of the force of gravity alone is called a ‘free fall’.

Question 16.
Suppose a planet exists whose mass and radius, both are half that of the earth. Calculate the acceleration due to gravity on the surface of this planet.
Answer:
On the surface of the earth, g = \(\frac{\mathrm{GM}}{\mathrm{R}^{2}}\)
On the surface of the planet, \(g^{\prime}=\frac{G\left(\frac{M}{2}\right)}{\left(\frac{R}{2}\right)^{2}}=\frac{2 G M}{R^{2}}=2 g\)

Question 17.
Define mass of a body. What is its SI unit?
Answer:
The mass of a body represents the quantity of matter contained in the body. It gives a measure of inertia of the body. The greater the mass of a body, the greater is its inertia. The SI unit of mass is kilogram (kg).

Question 18.
Define one kilogram – weight. How many newtons are there in 1kg wt?
Answer:
One kilogram – weight (kg – wt)
= 1kg × 9.8 m/s2 = 9.8 N.

Question 19.
State Archimedes’ principle.
Answer:
This principle states that when a body is immersed fully or partially in a fluid, it experiences an upward thrust equal to the weight of the fluid displaced by it.

Analysing & Evaluating Questions

Question 20.
A beam balance is used for measuring the mass of a body, whereas a spring balance gives the weight of a body. What is measured by a digital balance?
Answer:
Digital balance measures the weight of a body.

Question 21.
Under what conditions do the two hollow balls – one of aluminium and the other of iron, experience equal upthrust when placed in water?
Answer:
The two balls will experience equal upthrust in water when their volumes inside the water are equal.

Question 22.
The density of liquid B is greater than that of liquid A. A hydrometer is placed one by one in the two liquids. In which liquid will the hydrometer sink to the greater depth?
Answer:
The hydrometer will sink deeper in liquid A.

Short Answer Type Questions

Question 1.
During free – fall of an elevator, what is the weight of a body inside it? Give reasons for your answer.
Answer:
During free – fall of an elevator the apparent weight of the object becomes zero. This is because both the body and the elevator are in free fall, and have a downward acceleration of ‘g’. In this situation normal reaction on the body becomes zero. Since normal reaction is responsible for the sensation of weight in a body, the apparent weight of the body in this case becomes zero.

Question 2.
What is relative density?
Answer:
The relative density of a substance is the ratio of its density to that of the water at 4°C. Relative density Density of the substance Density of water at 4°C

Question 3.
Differentiate between ‘g’ and ‘G’ in tabular form.
Answer:

Acceleration due to gravity ‘g’ Universal gravitational constant ‘G’
(a) It is the acceleration acquired by a body due to earth’s gravitational pull on it. (a) It is numerically equal to the force of attraction between two masses of 1kg each separated by a distance of 1 m.
(b) ‘g’ is not a universal constant. It is different at different places on the surface of the earth. Its value varies from one celestial body to another. (b) ‘G’ is a universal constant and its value is same, i.e., 6.67 × 10-11 N m2 kg-2 everywhere in the universe.
(c) It is a vector quantity. (c) It is a scalar quantity.

Question 4.
Why is it easier to swim in sea water than in river water?
Answer:
The density of sea water is high due to dissolved salts in it as compared to the density of river water. Hence, the buoyant force applied on the swimmer by the sea water is high which helps in floating and makes swimming simpler.

Question 5.
A ship made of iron does not sink but an iron nail sinks in water. Why?
Answer:
The iron nail sinks because of its high density and less buoyant force acting on it due to lesser surface area. Whereas, the surface area of a ship is greater and thus experiences a higher buoyant force. Due to this fact, a ship floats but an iron nail sinks.

Question 6.
A stone and feather are thrown from a tower. Both the objects should reach the ground at the same time but it does not happen. Give reasons.
Answer:
As per the motion of objects due to gravitational pull of the earth, both the bodies are acted upon by the same force of the earth but the stone will fall first and then the feather. Feather being lighter, experiences greater air resistance, so it will reach later.

Question 7.
The relative density of gold is 18.3. The density of water is 103 kg/m3? What is the density of gold in S.I units?
Answer:
The relative density of gold is 18.3.
Relative density of gold = \(\frac{Density of gold}{Density of water}\)
That is, density of gold = Relative density of gold × Density of water = 18.3 × 103 kg/m3 = 18300 kg/m3.

Question 8.
The acceleration due to gravity at the moon’s surface is 1.67 m/s2. If the radius of the moon is 1.74 × 106m, calculate the mass of the moon.
Answer:
Here, G = 6.67 × 10-11 Nm2/kg2
g = 1.67 m/s2
R= 1.74 × 106 m.
Mass of the moon is
M = \(\frac{\mathrm{gR}^{2}}{\mathrm{G}}\) = \(\frac{1.67 \times\left(1.74 \times 10^{6}\right)^{2}}{6.67 \times 10^{-11}}\)
= 7.58 × 1022 kg.

Question 9.
Derive the formula for the gravitational force acting between two objects.
Answer:
Let two objects A and B of masses ‘M’ and’m’, lie at a distance d from each other as shown in the figure.
JAC Class 9th Science Solutions Chapter 10 Gravitation 2
Let the force of attraction between two objects be F.
According to the universal law of gravitation, the force between two objects is directly proportional to the product of their masses.
F ∝ Mm … (1)
And the force between two objects is inversely proportional to the square of the distance between them,
F ∝ \(\frac{1}{\mathrm{~d}^{2}}\) …………(2)
F ∝ \(\frac{\mathrm{Mm}}{\mathrm{d}^{2}}\)
where G is universal gravitational constant

Question 10.
Find the value of ‘g’, acceleration due to gravity.
Answer:
g = \( \frac{\mathrm{GM}}{\mathrm{R}^{2}}\)
G = 6.67 × 10-11 Nm2/kg2 (constant)
M = 6 × 1024 kg (mass of the earth)
= \( \frac{6.7 \times 10^{-11} \mathrm{Nm}^{2} / \mathrm{kg}^{2} \times 6 \times 10^{24} \mathrm{~kg}}{\left(6.4 \times 10^{6} \mathrm{~m}\right)^{2}}\)
= 9.8 m/s2

JAC Class 9 Science Important Questions Chapter 10 Gravitation

Question 11.
Camels can walk easily on desert sand but we are not comfortable walking on the sand. Why do you think so?
Answer:
The surface area of a camel’s feet is broad and large. Thus, the pressure exerted is low. However, when we walk, our legs sink because the pressure exerted by our body is not equally distributed but is directed towards the legs.

Question 12.
Define lactometer and hydrometer.
Answer:
Lactometer is a device used to find the purity of milk. Hydrometer is a device used to find the density of a liquid.

Question 13.
Two wood pieces of same size and mass are dipped in two beakers containing water and oil. One wood floats on water, but the other one sinks in oil. Why?
Answer:
The wood floats on water because the density of wood is lower than the density of water, and the other wood sinks in the oil because the density of wood is more than that of the oil.

Question 14.
What are fluids? Why is Archimedes’ principle applicable only for fluids? Give the applications of Archimedes’ principle.
Answer:
Liquids are the substances which can flow. Archimedes principle is based on the upward force exerted by fluids on any object immersed in them. Hence, it is applicable only for fluids. Applications of Archimedes’ principle are as follows:

  1. It is used to design ships and submarines.
  2. To determine the purity of milk using lactometers which are designed based on the Archimedes’ principle.
  3. To make hydrometers which are used to determine the density of liquids.

Question 15.
The volume of 60g of a substance is 10cm2. If the density of water is 1g/cm2, find out whether the substance will float or sink in water.
Answer:
Mass = 60g
Volume = 10 cm3
The density of water is 1g/cm2. As the density of the given substance is more than the density of water, the substance will get submerged in water.

Question 16.
What is meant by buoyancy?
Answer:
When a body is submerged in a fluid, the fluid exerts an upward force on the submerged body. This upward force is equal to the weight of the fluid displaced by the submerged body and is called the buoyant force. In other words, it is the force exerted by the fluid when an object is submerged in it.

Analysing & Evaluating Questions

Question 17.
Identical packets are dropped from two aeroplanes, one over the equator and the other over the north pole, both from the height h. Assuming that all conditions are identical, explain if those packets take same time to reach the surface of earth or not. Justify your answer.
Answer:
No. The two packets will take different time intervals to reach the earth’s surface. This is because the acceleration due to gravity (g) is greater at the poles than that at the equator. The packet will fall slowly at the equator than that at the north pole.

Question 18.
You must have seen two types of balances. A grocer has a balance with two platforms or pan, and a needle moving on a scale. Some junk dealers (kabadiwalas) may be using a spring balance to weigh used newspapers. Suppose, the two balances give the same measure for a given body on the earth. Now, you take the balances to the moon. Would the two balances give the same measure? Explain your answer.
Answer:
No. The two balances will not give the same measure on the moon. This is because, the spring balance measures the weight, and the grocer’s balance measures the mass. The weight of a body depends upon the acceleration due to gravity at the place of measurement. The acceleration due to gravity on the moon is not equal to that on the earth. Therefore, spring balance will give different readings relative to the grocer’s balance on the moon.

Long Answer Type Questions

Question 1.
What is centripetal force? From where does the moon get the centripetal force required for its motion around the earth?
Answer:

  1. Centripetal force When a body moves along a circular path with a uniform speed, its direction of motion changes at every point. The change in direction involves change in velocity or acceleration.
  2. The force that provides this acceleration and keeps the body moving along the circular path, acts towards the centre. This force is called centripetal (centre seeking) force.
  3. Therefore, a force which is required to make a body move along a circular path with uniform speed is called centripetal force. Centripetal force always acts along the radius and towards the centre of the circular path.
    JAC Class 9th Science Solutions Chapter 10 Gravitation 3
  4. The figure given here shows that it is the centripetal force which continuously deflects a particle from its straight line path to make it move along a circle.
  5. Example: The moon needs a centripetal force for its circular motion around the earth. This centripetal force is provided by the gravitational attraction exerted by the earth on the moon.

Question 2.
Show that the weight of an object on the moon is 1/6,h its weight on the earth. Given that the mass of the earth is 100 times the mass of the moon and its radius is 4 times that of the moon.
Answer:
Suppose, mass of the object = m
mass of the earth = Me
mass of the moon = Mm
radius of the earth = Re
radius of the moon = Rm
Then, Me = 100 Mm and Re = 4Rm
Weight of an object of mass m on the earth is
We = the force with which the earth
attracts the object = G \(\frac{\mathrm{M}_{\mathrm{e}} \mathrm{m}}{\mathrm{R}_{\mathrm{e}}^{2}}\)
Weight of the object on the moon is
Wm = The force with which the moon
attracts the object = \( \mathrm{G} \frac{\mathrm{M}_{\mathrm{m}} \mathrm{m}}{\mathrm{R}_{\mathrm{m}}^{2}}\)
\(\frac{W_{m}}{W_{e}}\) = \(\frac{\left(G \frac{M_{m} m}{R_{m}^{2}}\right)}{\left(G \frac{M_{m} m}{R_{e}^{2}}\right)}\)
= \(\frac{M_{m}}{M_{e}} \times \frac{\left(R_{e}\right)^{2}}{\left(R_{m}\right)^{2}}\)
= \(\frac{\mathrm{M}_{\mathrm{m}}}{100 \mathrm{M}_{\mathrm{m}}} \times \frac{4 \mathrm{R}_{\mathrm{m}}^{2}}{\mathrm{R}_{\mathrm{m}}^{2}}\) = \(\frac{16}{100} \approx \frac{1}{6}\)
Thus, the weight of an object on the moon is about one – sixth of its weight on the earth.

JAC Class 9 Science Important Questions Chapter 10 Gravitation

Question 3.
Briefly explain how can Archimedes’ principle be verified experimentally.
Answer:
According to Archimedes’ principle, when a body is immersed in a liquid, completely or partially, it loses its weight. The loss in weight is equal to the weight of liquid displaced by the body. The loss in weight of a body is due to the presence of upthrust which is equal to the weight of liquid displaced.
Thus, a Loss in weight = Weight of body in air – Weight of body immersed in water =
W W1 = upthrust in water on the body = Weight of liquid displaced.
JAC Class 9th Science Solutions Chapter 10 Gravitation 4
As shown in figure, measure the weight of a solid, say a metallic ball, in air using spring balance. Weigh the empty beakers using spring balance. Set the spring balance, overflow can with tap water and beaker. Now, allow the bob to immerse completely in water in overflow can. Note down the new position of the pointer of the spring balance.

This will give you the weight of the brass bob in tap water. It is found to be less than the weight of bob in air. Weigh the beaker containing displaced water which is collected from the overflow can while immersing the bob in it completely. It is observed that the loss in weight of the bob is equal to the weight of the water collected in the beaker, i.e., weight of the water displaced.

Question 4.
With the help of an activity, prove that the force acting on a lesser area exerts a larger pressure.
Answer:
Consider a block of wood kept on a tabletop. The mass of the wooden block is 5kg. Its dimensions are 30 cm × 20 cm × 10 cm.
Now, we have to find the pressure applied by the wooden block on the tabletop by keeping it vertically and horizontally.
JAC Class 9th Science Solutions Chapter 10 Gravitation 4
The mass of the wooden block = 5kg
Weight of the wooden block applies a thrust on the tabletop.
Thrust = F = mg = 5kg × 9.8 m/s2 = 49 N
(Case a) : When the wooden box is kept vertically with sides 20 cm × 10 cm,
Area of a side = length × breadth = 20 cm × 10 cm = 200 cm2 = 0.02m2
Pressure = \(\frac{Thrust}{Area}\) = \(\frac{49 \mathrm{~N}}{0.02 \mathrm{~m}^{2}}\)
= 2450 N/m2
JAC Class 9th Science Solutions Chapter 10 Gravitation 6
(Case b): When the block is kept horizontally with side 30 cm × 20 cm, Area = length × breadth = 30 cm × 20 cm = 600 cm2 = 0.06 m2

Pressure = \(\frac{Thrust}{Area}\) = [/latex] \frac{49 \mathrm{~N}}{0.02 \mathrm{~m}^{2}}[/latex]
= 816.7 N/m2
The pressure exerted by the box in case (a) in more as compared to the pressure exerted in case (b). The area is reduced and the pressure exerted is more.
This shows that pressure ∝= \( \frac{1}{\text { Area }}\)
Hence, pressure will be larger if the area is reduced.

Analysing & Evaluating Questions

Question 5.
(a) A cube of side 5 cm is immersed in water and then in saturated salt solution. In which case it will experience a greater buoyant force. If each side of the cube is reduced to 4 cm and then immersed in water, what will be the effect on the buoyant force experienced by the cube as compared to the first case for water.

(b) A ball of weight 4 kg and density 4000 kg m3 is completely immersed in water of density 103 kg m3. Find the force of buoyancy on it. (Given g = 10 ms-2)
Answer:
(a) The cube will experience greater buoyant force in salt solution. When the side of the cube is reduced to 4 cm, it will experience lesser buoyant force as compared to the first case.
This is because the volume of water displaced by the smaller cube is lesser than that displaced by the original cube,

(b) Volume of water displaced by the ball = Volume of the ball = \(\frac{Mass}{Density}\)
= \(\frac{4 \mathrm{~kg}}{4000 \mathrm{~kg} \mathrm{~m}^{-3}}\) = 10-3 m3
Weight of water displaced by the ball = Volume of water × Density × g
= 10-3 m3 × 103 kg m3 × 10 ms-2 = 10 N
So, Buoyant force acting on the ball = Weight of water displaced = 10 N

Activity 1

  • Take a piece of thread.
  • Tie a small stone at one end. Hold the other end of the thread and whirl it round.
  • Note the motion of the stone.
  • Now release the thread.
  • Again, note the direction of motion of the stone.
  • Record your observations and draw conclusion about the direction of the stone.
    JAC Class 9th Science Solutions Chapter 10 Gravitation 7
  • If thread is released when stone is here, stone goes straight towards A not towards B Top view A stone describing a circular path

JAC Class 9th Science Solutions Chapter 10 Gravitation 8

Observations

  • The motion gets accelerated and stone moves in a circular path.
  • When the thread is released, the stone makes a tangent to the circle and falls down.

ACTIVITY 2

  • Take a sheet of paper and a stone. Drop them simultaneously from the first floor of a building.
  • Observe whether both of them reach the ground simultaneously or not.

Observations

  • We see that the paper reaches the ground a little later than the stone. This happens because of air resistance. The air offers resistance due to friction to the motion of the falling objects. The resistance offered by air to the paper is more than the resistance offered to the stone.
  • If we do the experiment in a glass jar from which air has been sucked out, the paper and the stone would fall at the same rate.

ACTIVITY 3

  • Take an empty plastic bottle. Close the mouth of the bottle with an airtight stopper. Put it in a bucket filled with water and observe.
  • Push the bottle into the water and observe again. Try to push it further down.
  • Now, release the bottle. Record your observations.
  • Does the force due to the gravitational attraction of the earth act on this bottle? If so, why doesn’t the bottle stay immersed in water after it is released? How can you immerse the bottle in water?

Gravity
JAC Class 9th Science Solutions Chapter 10 Gravitation 9
Observations

  • The plastic bottle floats on water. When it is pushed deeper, the upward force on the bottle increases.
  • When released, the bottle bounces back to the surface because the upthrust on the bottle was larger than the downward pull of gravity
  • Take a piece of stone and tie it to one end of a rubber string or a spring balance.

ACTIVITY-4

  • Take a piece of stone and tie it to one end of a rubber string or a spring balance.
    Thread
    JAC Class 9th Science Solutions Chapter 10 Gravitation 10
  • Suspend the stone by holding the balance or the string as shown in the figure (A).
  • Note the elongation of the string or the reading on the spring balance due to the weight of the stone.
  • Now, slowly dip the stone in the water in a container as shown in Figure (B).
  • Observe what happens to the elongation of the string or the reading on the balance.

Observations

  • In fig. A, the elongation of the string is more.
  • In fig. B, when the stone is dipped in water, the length of the string is reduced.
  • The length of the string in case (B) decreases due to the upward force exerted by water on the stone called buoyant force.

Value Based Questions

Question 1.
Priya had a bad experience during the take off of the plane when she boarded it for the first time. Her friend assisted and helped her during the landing of plane. She told her to fasten the seat belt and involved her in gossip. Priya faced less problems while landing of the plane.
1. Why do we tie our seat belts in moving cars or during take off of the plane?
2. What is free fall?
3. What value of Priya’s friend is seen in this set?
Answer:

  1. We tie our seat belts to remain intact on the seat so that our body does not fall forward.
  2. When an object falls towards the earth under the gravitational force alone, we say that the object is in free fall.
  3. Priya’s friend showed the value of concerned, sympathetic, responsible and caring friend.

JAC Class 9 Science Important Questions Chapter 10 Gravitation

Question 2.
A goldsmith measured the purity of gold by using a special measuring device. He told the customer that there was impurity present in gold ornament that he wanted to buy and was not 22 carat but 18 carat jewellery.
1. How can we find the purity of gold?
2. What is the unit of relative density?
3. What value of goldsmith is reflected in this act?
Answer:

  1. The purity of gold can be obtained by knowing the density of the gold.
  2. Relative density does not have any unit.
  3. Goldsmith showed the value of honesty and trustworthiness.

JAC Class 9 Science Important Questions

JAC Class 9 Science Important Questions Chapter 9 Force and Laws of Motion

JAC Board Class 9th Science Important Questions Chapter 9 Force and Laws of Motion

Multiple Choice Questions

Question 1.
The SI unit of force is
(a) kg m/s
(b) newton
(c) dyne
(d) kg wt
Answer:
(b) newton

Question 2.
The combined effect of mass and velocity is taken into account by a physical quantity called
(a) torque
(b) momentum
(c) moment
(d) force
Answer:
(b) momentum

Question 3.
Quantitative definition of force is given by
(a) Newton’s first law of motion
(b) Newton’s second law of motion
(c) Newton’s third law of motion
(d) Newton’s law of gravitation
Answer:
(b) Newton’s second law of motion

Question 4.
Momentum gives a measure of
(a) mass
(b) weight
(c) velocity
(d) motion
Answer:
(d) motion

Question 5.
An athlete runs some distance before taking a long jump because
(a) he gains energy to take himself through long distance
(b) it helps him to apply a larger force
(c) by running, action and reaction forces increase
(d) by running, the athlete gives himself larger inertia of motion
Answer:
(d) by running, the athlete gives himself larger inertia of motion

Question 6.
Rocket works on the principle of conservation of
(a) velocity
(b) energy
(c) linear momentum
(d) mass
Answer:
(c) linear momentum

Question 7.
The rate of change of momentum of an object is proportional to the
(a) mass of the body
(b) velocity of the body
(c) net force applied on the body
(d) none of these
Answer:
(c) net force applied on the body

JAC Class 9 Science Important Questions Chapter 9 Force and Laws of Motion

Question 8.
A force of 50 N moves a body. Which of the following is correct?
(a) Frictional force exerted on the body is less than 50N
(b) Frictional force exerted on the body is more than 50N
(c) None of these
(d) Both (a) and (b)
Answer:
(a) Frictional force exerted on the body is less than 50N

Question 9.
If a football and a stone have same mass, then both will have
(a) same inertia
(b) same momentum
(c) different inertia
(d) different momentum
Answer:
(a) same inertia

Question 10.
The rate of change of momentum w. r. t time is measured in
(a) kg m
(b) kg
(c) kg ms-1
(d) kg ms-1
Answer:
(d) kg ms-1

Question 11.
A block of mass M is pulled with a force F along a smooth horizontal surface with a rope of mass m. The acceleration of the block will be
(a) F/M
(b) F/m
(c) F/(M + m)
(d)F/(M – m)
Answer:
(c) F/(M + m)

Question 12.
Action and reaction forces act on two
(a) different objects
(b) same objects
(c) either (a) or (b)
(d) none of these
Answer:
(a) different objects

Question 13.
A man is standing in a boat in still water. If he tries to walk towards the shore, the boat will
(a) move away from the shore
(b) remain stationary
(c) sink
(d) move towards the shore
Answer:
(a) move away from the shore

Question 14.
When an object undergoes acceleration
(a) its speed always increases
(b) its velocity always increases
(c) it always falls towards the earth
(d) a force always acts on it
Answer:
(d) a force always acts on it

Question 15.
On applying a constant force to a body, it moves with uniform
(a) momentum
(b) speed
(c) acceleration
(d) velocity
Answer:
(c) acceleration

Analysing & Evaluating Questions

Question 16.
A goalkeeper in the game of football pulls his hands backwards after holding the ball shot at the goal. This enables the goal keeper to
(a) exert larger force on the ball
(b) reduce the force exerted by the ball on hands
(c) increase the rate of change of momentum
(d) decrease the rate of change of momentum
Answer:
(b) reduce the force exerted by the ball on hands

Question 17.
A passenger in a moving train tosses a coin which falls behind him. It means that motion of the train is
(a) accelerated
(b) uniform
(c) retarded
(d) along circular tracks
Answer:
(a) accelerated

JAC Class 9 Science Important Questions Chapter 9 Force and Laws of Motion

Question 18.
An object of mass 2kg is sliding with a constant velocity of 4 ms-1 on a frictionless horizontal table. The force required to keep the object moving with the same velocity is
(a) 32 N
(b) 0 N
(c) 2 N
(d) 8 N
Answer:
(b) 0 N

Assertion Reason Questions

Directions: In the following questions, the Assertions and the Reasons have been put forward Read the statements carefully and choose the correct alternative from the following:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.
(C) The assertion is true but the reason is false.
(D) Both statements are false.
1. Assertion: A brick has more inertia than a hollow wooden block of the same shape and size.
Reason: Heavier the body, more is the inertia.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

2. Assertion: A body falling towards the earth also pulls the earth towards itself.
Reason: The forces always occur in pairs.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

3. Assertion: When a bus starts, the person inside it falls forward.
Reason: The bus pushes the person forward.
Answer:
(D) Both statements are false.

4. Assertion: The third law of motion defines acceleration.
Reason: The third law of motion states that the net force experienced by a body is proportional to the rate of change in momentum of the body.
Answer:
(D) Both statements are false.

5. Assertion: Action and reaction forces are always equal and opposite.
Reason: Action and reaction forces cancel each other.
Answer:
(C) The assertion is true but the reason is false.

Very Short Answer Type Questions

Question 1.
Define force.
Answer:
Force may be defined as a push or a pull which changes or tends to change the state of rest or of uniform motion or direction of motion of a body.

Question 2.
Define one Newton.
Answer:
One newton is the force which produces an acceleration of m/s2 in an object of mass 1kg.
1N = 1kg m/s2

Question 3.
State the various effects of force.
Answer:
A force applied on an object can do five things:
(a) It can change the speed of the object.
(b) It can change the direction of motion of the object.
(c) It can change the shape and size of the object.
(d) It can set an object at rest in motion.
(e) It can bring a moving object to rest.

Question 4.
Define resultant force.
Answer:
The resultant force or resultant of several forces acting simultaneously on a body is that single force which produces the same effect on a body as all these forces produce together.

JAC Class 9 Science Important Questions Chapter 9 Force and Laws of Motion

Question 5.
What is frictional force?
Answer:
The force that always opposes the motion of an object is called force of friction.

Question 6.
What is inertia?
Answer:
The natural tendency of an object to resist a change in their state of rest or of uniform motion along a straight line is called inertia.

Question 7.
State Newton’s first law of motion.
Answer:
An object remains in its state of rest or of uniform motion in a straight line unless acted upon by an external unbalanced force.

Question 8.
Place a water – filled tumbler on a tray. Hold the tray and turn around as fast as you can. We observe that the water spills. Why?
Answer:
The water spills when the tray turns around fastly, because initially, the water filled in the tumbler placed on the tray was in a state of rest. While turning, we apply force on the tray which starts moving but the water remains at rest due to its inertia, and hence, it spills out of the tumbler.

Question 9.
State Newton’s second law of motion.
Answer:
The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of the force.

Question 10.
State Newton’s third law of motion.
Answer:
To every action, there is an equal and opposite reaction and they act on two different bodies.

Question 11.
Why are shockers used in cars, scooters and motorcycles?
Answer:
Due to the shockers, the time interval of the jerk increases. As the rate of change of momentum will be smaller, comparatively less force acts on the passengers during the jerks.

Question 12.
Why is glass or chinaware packed with straw?
Answer:
The straw paper between the chinaware increases the time of experiencing the jerk during transportation. Hence, they strike against each other with a less force and are less likely to be damaged.

Question 13.
A bird hit the windscreen of a fast moving car and fell on the bonnet. Which of the two, the car or the bird, suffers greater change in momentum?
Answer:
By the law of conservation of momentum, both the car and the bird suffered equal and opposite change in momentum.

Question 14.
What decides the rate of change of momentum of an object?
Answer:
The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of force.

Question 15.
The diagram shows a moving truck. Forces A, B, C and D are acting on the truck. Name the type of each of these forces acting on the truck.
JAC Class 9th Science Solutions Chapter 9 Force and Laws of Motion 1
Answer:
The forces A, B, C and D acting on the truck are:
A driving force
B normal reaction
C frictional force
D weight gravitational force.

Analysing & Evaluating Questions

Question 16.
Two identical bullets are fired, one by a light rifle and another by a heavy rifle, with the same force. Which rifle will hurt the shoulder more and why?
Answer:
The velocity of recoil will be higher for ligher rifle. So lighter rifle will hurt the shoulder more.

Question 17.
When a fast moving carrom striker hits the carrom coin at the bottom of a pile, ¡t moves out without disturbing
the pile. Which kind of inertia of the pile is responsible for it?
Answer:
Inertia of rest of the pile is responsible for it.

Question 18.
There are three solid balls made up of aluminium, steel and wood, of the same shape and same volume. Which of them would have the highest inertia?
Answer:
Steel ball will have the highest inertia This is because the density of steel is higher than aluminium and wood As a result, the steel ball will have the highest mass and hence highest inertia

Short Answer Type Questions

Question 1.
Differentiate between balanced and unbalanced forces.
Answer:

Balanced forces Balanced forces
1. The resultant of balanced forces is zero. 1. The resultant of balanced forces is zero.
2. These forces donot produce anyacceleration in the body. 2. These forces donot produce anyacceleration in the body.
3. Example: A book kept on the table (the downward force of gravity on the book is balanced by the normal reaction by the table on the book in upward direction). 3. Example: When the book that is kept on the table is pushed to the left side (the book moves as the push towards left is greater than the frictional force acting towards right).

Question 2.
Give examples to show that balanced forces can change the shape of an object.
Answer:
Consider a spring attached to a rigid support at one of its ends, as shown in the figure.
JAC Class 9th Science Solutions Chapter 9 Force and Laws of Motion 2
If we pull the free ends of the spring, it gets elongated Thus, on applying force, a spring expands. Similarly, if we hold a rubber ball between our palms and push the two palms against each other, we find that the ball is no longer round but oblong. The force exerted on the ball changes its shape, as shown in the figure. In both cases, the two forces, being equal and opposite, balance each other but change the shape of the object.

Question 3.
A football player kicks the ball which travels in the air for a while and lands on the ground where the ball travels on the ground for a short distance and then stops. What may be the reason behind it?
Answer:
The reason is frictional force. There is always a contact between the ball and the ground The opposing force always acts against the motion of the ball, thereby stopping the ball.

JAC Class 9 Science Important Questions Chapter 9 Force and Laws of Motion

Question 4.
A table is moved across the floor with a constant velocity where the horizontal force acting on it is 400N. What will be the frictional force that will be acting on the table?
Answer:
According to Newton’s third law of motion, for every action there will be an equal and opposite reaction. The net force acting on the table is zero because the table moves with constant velocity in forward direction. Hence, an equal amount of frictional force must act in opposite direction as that of the table, i.e., F = – 400N.

Question 5.
When the car, we are moving in, makes a sharp turn at a very high speed, we tend to get thrown to one side. Explain the statement.
Answer:
The reason behind this is the law of inertia While moving in a car along a straight line, we tend to maintain our state of motion. But when the car takes a sharp turn, our bodies resist the change in direction and are thrown to the opposite side due to inertia.

Question 6.
Athletes always have a special posture by resting their right foot on a solid support, why?
Answer:
During the race, athletes have to run the heats and they rest their right foot on the solid support before the start, so that this support can give them a lot of force during the start of the race. They push the support backwards and get an equal and opposite forward push to get a very good start.

Question 7.
The safety belts in the car help in preventing accidents. Justify the statement.
Yes, safety belts help in preventing accidents. When a car is moving with a high speed, our body tends to be in movement due to inertia of motion in the forward direction. So when there is a sudden  collision, serious injuries can happen. However, seat belts exert a force on our body to slow down the forward motion and hence prevent injuries.

Question 8.
A karate player breaks the pile of tiles with a single blow. Give reason.
Answer:
A karate player strikes the pile of tiles by applying a very large velocity. The overall momentum of fast moving hand is reduced to zero in a very short interval. So this increases the rate of change of momentum which increases the force on the tiles and they eventually break.

Question 9.
Athletes are made to fall on a sand bed while performing a high jump. Give reason.
Answer:
During the high jump event, an athlete is made to fall on the sand bed because it increases the time to attain the rest
position. We know that, F = \(\frac{m(v-u)}{t}\)
So, force and time are inversely proportional to each other. If there is an increase in time, there is a decrease in rate of change of momentum and therefore the force or the impact is reduced This prevents injuries to the feet of athlete.

Question 10.
Explain the law of conservation of momentum.
Answer:
According to the law of conservation of momentum, the total momentum of the objects before collision is equal to the total momentum after collision, provided there is no external unbalanced force acting on them.

JAC Class 9 Science Important Questions Chapter 9 Force and Laws of Motion

Question 11.
A bullet of mass 20g moving with a speed of 500 ms-2 strikes a wooden block of mass 1kg and gets embedded in it. Find the speed with which the block moves along with the bullet.
Answer:
Let the final velocity of the block along with the bullet embedded in it be v.
For bullet, m1 = 20g = 0.02 kg,
U1 = 500 m/s, v1 = v
For block, m1 = 1kg, u2= 0, v2 = v
According to the law of conservation of momentum,
Total momentum before collision = Total momentum after collision
m1u1 + m2u2 = m1v1 + m2v2
m1u1 + m2u2= (m1 + m2) v
v = \(\frac{m_{1} u_{1}+m_{2} u_{2}}{m_{1}+m_{2}}\)
= \(\frac{(0.02 \times 500)+(1 \times 0)}{(0.02+1)}\)
=\(\frac{10}{1.02}\) = \(\frac{1000}{102}\)
= 9.8 m/s.

Analysing & Evaluating Questions

Question 12.
Two balls of the same size but of different materials, rubber and iron, are kept on the smooth floor of a moving train. The brakes are applied suddenly to stop the train. Will the balls start rolling? If so, in which direction? Will they move with the same speed?

Answer:
The balls will start rolling in the forward direction. No. The two balls will move with different speed This is because the inertia of the two balls is not the same.

Question 13.
Two forces F1 = 40N and F2 = 60N are acting on an object as shown in the figure.
JAC Class 9th Science Solutions Chapter 9 Force and Laws of Motion 3
1. What is the net force acting on the object?
2. What is the direction of the net force acting on the object?
3. How much extra force is acting on the object if the object is not moving due to the application of these two forces? Name that force. Where does that force act and what is the direction of that force?
Answer:

  1. Net force on the object = 60N – 40N = 20N
  2. Net force of 20N acts in the direction of F2 (i.e., towards left)
  3. A force equal to 20N is acting on the object.
    This force is the frictional force. This force acts in the direction of F1

Long Answer Type Questions

Question 1.
Describe Galileo’s experiments with inclined planes and state their conclusion.
Answer:
By observing the motion of objects on inclined planes, Galileo deduced that objects move with constant speed when no force acts on them.
JAC Class 9th Science Solutions Chapter 9 Force and Laws of Motion 4

  1. In the first experiment, Galileo studied the motion of marbles on an inclined plane. He observed that when a marble rolls down an inclined plane, its velocity increases, as shown in the figure A.
  2. Here the marble falls under the unbalanced force of gravity. The velocity of the marble decreases when it rolls up the inclined plane (against the force of gravity), as shown in the figure B.
  3. From these observations, Galileo argued that the velocity of a marble rolling on a flat horizontal surface should remain constant. To test his idea, Galileo used double inclined planes.
  4. He observed that when the inclinations of the planes on both sides were equal, the marble rolled down from one plane from a certain height will climb up to the same height on the other plane.
    JAC Class 9th Science Solutions Chapter 9 Force and Laws of Motion 5
    side plane were gradually decreased, the marble would travel larger and larger distances to reach the same height.
  5. Ultimately, if the right side plane were made horizontal, the marble would continue to travel forever to reach the same height from which it was released No unbalanced force acts on the marble in this case.
  6. The above experiment suggests that an unbalanced force (external force) is required to change the motion of an object while no unbalanced force is needed to keep an object moving with a constant velocity.
  7. In actual practice, the bodies stop due to the force of friction which always acts opposite to the direction of motion.

Question 2.
Mathematically explain the concept of conservation of momentum during collision between two bodies.
Answer:
Let us consider two bodies, viz., A and B, moving with initial velocities uA and uB respectively, such that uA > uB.
Let mass of body A be mA and that of B be mB.
Before collision
For body A, momentum = mAuA
For bodv B. momentum = mBuB
JAC Class 9th Science Solutions Chapter 9 Force and Laws of Motion 6
After collision, the bodies A and B move with velocities, say, vA and vB respectively. Let the collision occur for a time, say, t.
After collision
For body A, momentum = mAvA
For body B, momentum = mBvB
The rate of change of momentum for the body A = \(\frac{m_{A}\left(v_{A}-u_{A}\right)}{t}\)
The rate of change of momentum for the body A = \(\frac{m_{B}\left(v_{B}-u_{B}\right)}{t}\)
JAC Class 9th Science Solutions Chapter 9 Force and Laws of Motion 7
According to Newton’s third law of motion, The force FAB exerted by ball A on ball B and the force FBA exerted by the ball B on ball A must be equal and opposite to each other. Therefore
\(\left\{\frac{m_{A}\left(v_{A}-u_{A}\right)}{t}=-\left(\frac{m_{B}\left(v_{B}-u_{B}\right)}{t}\right)\right\}\)
mAuA + mBuB= mAvA + mBvB
Here, (mAuA + mBuA) is the total momentum of the two bodies, A and B, before collision and (mAvA+ mBvB) is the total momentum of the two bodies, A and B, after collision. So, the total momentum of the two bodies remains constant during collision, when no external force acts on them.

JAC Class 9 Science Important Questions Chapter 9 Force and Laws of Motion

Question 3.
Give some examples of Newton’s third law of motion.
Answer:
Newton’s third law of motion states that: For every action, there is always an equal and opposite reaction acting on two different bodies.
Examples:

  1. The person who is swimming, pushes the water backward (action), while water pushes the person forward (reaction).
  2. When a bullet is fired from a gun, the gun exerts a force on the bullet (action), the bullet exerts an equal and opposite force on the gun (reaction),
  3. When a rower jumps out of the boat in the forward direction (action), the boat moves backward (reaction).

Question 4.
Define the term ‘inertia’. Explain its types and state some of its examples in daily life.
Answer:

  1. The tendency of a body to resist change in its state of rest or of uniform motion is called inertia.
    • Inertia of rest: The ability of a body to resist any change in its state of rest.
    • Inertia of motion: The ability of a body to resist any change in its state of uniform motion.
    • Inertia of direction: The ability of a body to resist any change in its direction of motion.
  2. Examples of application of inertia in our day to day life are as follows:
    • When a carpet is beaten with a stick, the dust falls down.
    • When the car applies a sudden brake, we tend to fall forward.
    • When a bus suddenly takes a turn, we fall in the direction opposite to the turn.

Question 5.
Mathematically explain the concept of Newton’s second law of motion and also explain its importance in sports.
Answer:
Newton’s second law of motion: The rate of change of momentum of an object is directly proportional to the applied unbalanced force and it acts in the direction of force.

Example: Let us consider an object of mass (m), moving along a straight line with an initial velocity (u). Suppose, it attains a final velocity (v) in time (t).
Initial momentum of the object
= p1 = mu
Final momentum of the object
= p2 = mv
The change in momentum
= p2 – p1 = (mv) – (mu) = m (v – u)
The rate of change in momentum
= \(\frac{\mathrm{m}(\mathrm{v}-\mathrm{u})}{\mathrm{t}}\)
Therefore,
The applied force, F is
F ∝ \(\frac{\mathrm{m}(\mathrm{v}-\mathrm{u})}{\mathrm{t}}\)
F = \(\frac{\mathrm{mk}(\mathrm{v}-\mathrm{u})}{\mathrm{t}}\) …………..(i)
(where k is proportionality constant)
From the first equation of motion,
v = u + at
Substituting (ii) in (i),
So, F = kma
The unit of force is so chosen that the value of k becomes one.
Hence, F = kma or
F = ma
The second law is related to sports in the following examples:
(a) In a cricket match, a fielder who is trying to attempt a catch, generally pulls his hands along the moving ball because it consumes time to bring the momentum of the ball to zero. This decreases the rate change of mometum, and hence the force. So, when the time is increased, the overall force reduces, thus saving the hand from getting injured.

(b) In a high jump athletic event, the athletes are made to fall on a sand bed to increase the time of the athlete’s fall to stop after making the jump.
This decreases the rate of change of momentum and hence the force,

(c) A karate expert breaks a slab of ice with a single blow as he moves his hand very fast and then stops it in a very short time. Since the rate of change of momentum increases, the force also increases and the ice slab breaks.

Analysing & Evaluating Questions

Question 6.
A test tube containing little water is corked and suspended from two strings in a slanting position. Afterwards, the test tube is heated Answer the following:
JAC Class 9th Science Solutions Chapter 9 Force and Laws of Motion 8
1. What happens to the cork?
2. In which direction does the test tube move?
3. Compare the velocities of the cork and of the recoiling test tube.
Answer:

  1. On heating, the water inside the test tube vaporises and the cork is blown out.
  2. The test tube moves in the direction opposite to the direction in which the cork has blown out.
  3. Cork blows out with greater velocity than the recoiling test tube.

Activity 1

  • Make a pile of similar carom coins on a table, as shown in the figure.
  • Attempt a sharp and strong horizontal hit at the bottom of the pile using another carom coin or striker.

JAC Class 9th Science Solutions Chapter 9 Force and Laws of Motion 9
Observations

  • If the hit is strong enough the bottom coin moves out quickly.
  • Once the lowermost coin is removed, the inertia of the other coins makes them fall vertically on the table.

Activity 2

  • Set a five – rupee coin on a stiff card covering an empty glass tumbler standing on a table as shown in the figure.
  • Give the card a sharp horizontal flick with a finger.

JAC Class 9th Science Solutions Chapter 9 Force and Laws of Motion 10
Observations

  • If we do it fast, the card shoots away, allowing the coin to fall vertically into the glass tumbler due to its inertia.
  • The inertia of the coin tries to maintain its state of rest even when the card is flown away.
  • The force applied on the card due to flicking changes the inertia of the card but the coin resists this change and stays at rest, i.e, due to the inertia and gravity, the coin falls down into the tumbler.

JAC Class 9 Science Important Questions Chapter 9 Force and Laws of Motion

Activity 3

  • Request two children to stand on two separate carts as shown in the figure.
    JAC Class 9th Science Solutions Chapter 9 Force and Laws of Motion 11
  • Give them a bag full of sand or some other heavy object.
  • Ask them to play a game of catch with the bag and observe.
  • You can paint a white line on cartwheels to observe the motion of the two carts when the children throw the bag towards each other.

Observations

  • In this case, each of them receives an instantaneous reaction as a result of throwing the sand bag.
  • This activity explains Newton’s third law of motion, i.e., a force is exerted in forward direction in throwing the bag full of sand and the person who is throwing it, gets pushed backward.

Activity 4

  • Take a big rubber balloon and inflate it fully.
  • Tie its neck using a thread Also, using adhesive tape, fix a straw on the surface of this balloon.
  • Pass a thread through the straw and hold one end of the thread in your hand or fix it on the wall.
  • Ask your friend to hold the other end of the thread or fix it on a wall at some distance.
  • The arrangement is shown in the figure.
  • Now, remove the thread tied on the neck of the balloon and let the air escape from the mouth of the balloon.
  • Observe the direction in which the straw moves.

JAC Class 9th Science Solutions Chapter 9 Force and Laws of Motion 12
Observations.

  • When the air escapes out from the balloon, the straw moves in the direction opposite to the direction in which the air moved out of the balloon. This activity explains the law of conservation of momentum.
  • This activity is also based on Newton’s third law of motion, i.e., for every action, there is always an equal and opposite reaction between two bodies.

Value Based Questions

Question 1.
Class IX students were playing cricket with cork ball in the school campus. Abhishek, senior student, told them about the accidents that can occur due to cork ball in the campus and also advised them to bring a soft cosco ball to play the game.
1. Why is it safe to play with a soft ball and not with a hard cork ball?
2. A player pulls his hands backwards while catching the ball shot at high speed Why?
3. What value of Abhishek is seen in this act?
Answer:

  1. The soft ball has less inertia as compared to the heavy ball and it would not hurt the players.
  2. By pulling the hand backwards, it reduces the force exerted by the ball
    on the hand.
  3. Abhishek showed the value of being responsible and helpful by nature.

Question 2.
Rahul saw his karate expert friend breaking a brick. He tried to break the brick but his friend stopped him from doing so and told him that it would hurt him as one needs a lot of practice in doing so.
1. How can a karate expert break the brick without any injury to his hand?
2. What is Newton’s third law of motion?
3. What value of Rahul’s friend is seen in the above case?
Answer:

  1. A karate expert applies the force with a large velocity in a very short interval of time on the brick, therefore, a large force is exerted on the brick and it breaks.
  2. To every action there is an equal and opposite reaction, both act on different bodies.
  3. Rahul’s friend showed the value of being responsible and caring friend.

JAC Class 9 Science Important Questions

JAC Class 9 Science Important Questions Chapter 8 Motion

JAC Board Class 9th Science Important Questions Chapter 8 Motion

Multiple Choice Questions

Question 1.
Which of the following is correct for a car which travels a distance of 100 km in 2 hours?
(a) Its average speed is 50 km/h
(b) The car did not travel at 50 km/h all the time
(c) The car travelled at 50 km/h all the time
(d) All of the above
Answer:
(a) Its average speed is 50 km/h

Question 2.
The distance-time graph of an object shown in the given figure represents that the object is
(a) at rest position
(b) moving with constant speed
(c) moving with constant velocity
(d) moving with constant acceleration
Answer:
(a) at rest position

Question 3.
The SI unit of velocity is
(a) ms-1
(b) ms-2
(c) ms-3
(d) Nn-1
Answer:
(a) ms-1

Question 4.
Deceleration of a body is expressed in
(a) m
(b) ms-1
(c) ms-2
(d) ms-3
Answer:
(c) ms-2

JAC Class 9 Science Important Questions Chapter 8 Motion

Question 5.
The initial velocity of a body is ‘u’. It is under uniform acceleration ‘a’. Its velocity ‘v’ at any time ‘t’ is given by
(a) v = u + at2
(b) v = u + \(\frac{1}{2}\) at2
(c) v = u + at
(d) v = u
Answer:
(c) v = u + at

Question 6.
A wooden slab starting from rest, slides down a 10m long inclined plane with an acceleration of 5 ms-2 What would be its speed at the bottom of the inclined plane?
(a) 10 ms-1
(b) 12ms-1
(c) 10 cm-1
(d) 12 cm-1
Answer:
(a) 10 ms-1

Question 7.
The velocity of a particle increases from ‘u’ to ‘v’ in time’t’ during which it covers a distance ‘s’. If the particle has a uniform acceleration, which of the following equations does not apply to the motion?
(a) 2s = (v + u) t
(b) v2 = u2 – 2as
(c) a = v – u/t
(d) s = (u + \(\frac{1}{2}\) at) t
Answer:
(b) v2 = u2 – 2as

Question 8.
In 12 minutes, a car whose speed is 35 km/h travels a distance of
(a) 7 km
(b) 3.5 km
(c) 2.4 km
(d) none of these
Answer:
(a) 7 km

Question 9.
The area under the distance – time graph gives
(a) uniform speed
(b) non – uniform speed
(c) velocity and speed
(d) both (a) and (b)
Answer:
(d) both (a) and (b)

Question 10.
The odometer of a car measures
(a) speed
(b) velocity
(d) acceleration
(d) distance
Answer:
(d) distance

Question 11.
If a particle moves with a constant speed, the distance time graph is a
(a) straight line
(b) curved line
(c) straight line parallel to time axis
(d) straight line parallel to velocity axis
Answer:
(a) straight line

Question 12.
An object moving with uniform circular motion shows
(a) constant acceleration in speed
(b) constant velocity
(c) constant acceleration in direction
(d) constant change in type of motion
Answer:
(c) constant acceleration in direction

Question 13.
The slope of speed – time graph gives
(a) speed
(b) velocity
(c) acceleration
(d) momentum
Answer:
(c) acceleration

Question 14.
The distance travelled by a freely falling body is proportional to the
(a) mass of body
(b) square of the time of fall
(c) square of the acceleration due to
Answer:
(b) square of the time of fall

JAC Class 9 Science Important Questions Chapter 8 Motion

Question 15.
The figure shows the displacement time graph of a body moving in a straight line. The velocity of the body during the
JAC Class 9th Science Solutions Chapter 8 Motion 12
(a) 2 ms-2
(b) zero
(c) 3 ms-1
(d) 2.5 ms-1
Answer:
(b) zero

Analysing & Evaluating Questions

Question 16.
In which of the following cases of motion, the distance moved and the magnitude of displacement are equal?
(a) If the car is moving on a straight road
(b) If the car is moving in a circular path
(c) The pendulum is moving to and fro
(d) The earth is revolving around the Sun
Answer:
(a) If the car is moving on a straight road

Question 17.
Four cars A, B, C and D are moving on a levelled road. Their distance versus time graphs are shown here. Choose the correct statement.
JAC Class 9th Science Solutions Chapter 8 Motion 13
(a) Car A is faster than car D
(b) Car B is the slowest
(c) Car D is faster than car C
(d) Car C is the slowest
Answer:
(b) Car B is the slowest

Question 18.
Suppose a boy is enjoying a ride on a merry – go – round which is moving with a constant speed of 10 ms-1. It implies that the boy is
(a) at rest
(b) moving with no acceleration
(c) in accelerated motion
(d) moving with uniform velocity
Answer:
(c) in accelerated motion

Assertion Reason Questions

Directions: In the following questions, the Assertions and the Reasons have been put forward. Read the statements carefully and choose the correct alternative from the following:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.
(C) The assertion is true but the reason is false.
(D) Both the statements are false.

1. Assertion: Velocity is a scalar quantity.
Reason: Velocity cannot be zero.
Answer:
(D) Both the statements are false.

2. Assertion: A body moving in a circular path is in non – uniform motion.
Reason: The direction of a body moving in a circular path changes at every point.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

3. Assertion: A stone thrown vertically upwards has negative acceleration.
Reason: The acceleration of the stone thrown upward is in the direction opposite to the direction of its motion.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

4. Assertion: A freely falling body is in uniform motion.
Reason: A freely falling body covers equal distances in equal intervals of time.
Answer:
(D) Both the statements are false.

5. Assertion: An object under acceleration can have a uniform speed.
Reason: Both speed and acceleration are scalar quantities.
Answer:
(C) The assertion is true but the reason is false.

Very Short Answer Type Questions

Question 1.
Define uniform motion.
Answer:
If an object covers equal distances in equal intervals of time, however small the time intervals may be, the motion of the object is said to be uniform motion.

Question 2.
Define non – uniform motion.
Answer:
If an object covers unequal distances in equal intervals of time, it is said to be in ‘non – uniform motion’.

Question 3.
Define speed.
Answer:
It is the distance travelled by a body per unit time.
Speed. = \(\vec{a}\)

Question 4.
Define average speed.
Answer:
The total distance travelled by an object divided by the total time taken is called its average speed.

JAC Class 9 Science Important Questions Chapter 8 Motion

Question 5.
Define acceleration.
Answer:
It is defined as the rate of change of velocity with time.
Acceleration = \(\frac{Change in velocity}{Time Taken}\)
or a = \(\frac{v-\mathbf{u}}{t}\)
The SI unit of acceleration is m/s2.

Question 6.
Draw a distance – time graph that represents uniform speed.
Answer:
JAC Class 9th Science Solutions Chapter 8 Motion 14

Question 7.
With the help of a distance – time graph show that the object is stationary.
Answer:
JAC Class 9th Science Solutions Chapter 8 Motion 15

Question 8.
Define uniform circular motion.
Answer:
When a body moves in a circular path with uniform speed, its motion is called uniform circular motion.

Question 9.
Define scalar quantities. Give examples.
Answer:
The physical quantities which require only magnitude, and not the direction, for their complete description are called ‘scalars’ or ‘scalar quantities’. Distance, speed, time, area, etc., are all scalar quantities.

Question 10.
Define vector quantities. Give examples.
Answer:
The physical quantities which need both magnitude and direction for their complete description are called ‘vectors’ or vector quantities. Displacement, velocity, force, etc., are all vector quantities.

Question 11.
What is the SI unit of displacement?
Answer:
Metre (m).

Question 12.
A particle moves over three – quarters of a circle of radius. What is the magnitude of its displacement?
Answer:
When the particle covers three quarters of a circle, the magnitude of its displacement is
JAC Class 9th Science Solutions Chapter 8 Motion 16
AB = \(\sqrt{\mathrm{OA}^{2}+\mathrm{OB}^{2}}\) = \(\sqrt{r^{2}+r^{2}}\)
= \(\sqrt{2 r}\) = √2 r

Question 13.
Can the average speed of a moving body ever be zero?
Answer:
Speed is a scalar quantity and is always positive. So the average speed of a moving body can never be zero.

Question 14.
What is the relationship between the distance travelled and the time elapsed for motion with uniform velocity?
Answer:
Distance is directly proportional to the time elapsed. In fact,
Distance travelled = Uniform velocity × Time elapsed

Question 15.
What is the SI unit of acceleration?
Answer:
The SI unit of acceleration is m/s2.

Question 16.
What is acceleration of a body moving with uniform velocity?
Answer:
The acceleration of a body moving with uniform velocity is zero.

Question 17.
State a relationship connecting u, v, a and t for an accelerated motion. Give an example of motion in which acceleration is uniform.
Answer:
The relationship between u, v, a and t is v = u + at A body falling freely towards the earth has a uniform acceleration of 9.8 ms-2.

Question 18.
Express the velocity of a body in uniform circular motion in terms of its time period T.
Answer:
Suppose a body of mass m rotates in a circle of radiusr with velocity v. It completes one revolution in time T. Then,
Velocity = \(\frac{Distance}{Time}\)[/latex] = \(\frac{Circumference}{Time period }\)[/latex]
or v = \(\frac{2 \pi \mathrm{r}}{\mathrm{T}}\)

Analysing & Evaluating Questions

Question 19.
The cars A, B, C and D are moving on a levelled road. Their distance versus time graphs are shown in the figure. Which car is the slowest?
Answer:
Speed = Slope of distance – time graph. The smaller the slope, the smaller is the speed
JAC Class 9th Science Solutions Chapter 8 Motion 17
From the given figure, slope is minimum for car D. So, D is the slowest car.

Question 20.
A rubber ball dropped from a certain height bounce to certain height. This height keeps decreasing in subsequent bounces. What type of motion does the ball exhibit?
Answer:
The ball exhibits non – uniform motion.

JAC Class 9 Science Important Questions Chapter 8 Motion

Question 21.
A vehicle is moving at a constant velocity of 10 km/h in the north – south direction. It turns and starts moving towards east. What is the velocity of the vehicle towards east before taking the turn?
Answer:
Zero. The component of velocity at right angle to the original direction of motion is zero.

Short Answer Type Questions

Question 1.
Define the term rest and motion.
Answer:

  • Rest: If a body does not change its position with respect to its surroundings, the body is said to be at rest, e.g., a table lying in a room is at rest with respect to the walls of the room.
  • Motion: A body is said to be in motion if it changes its position with respect to its surroundings, e.g., a car running on the road is in motion with respect to the lamp posts, trees or bus stop on the roadside.

Question 2.
What is meant by a point object? Give some examples.
Answer:
Whenever the size of the object is much smaller than the distance it moves in a given time interval, the size of the object can be neglected. The object can be regarded as a point object in such cases.
Examples:

  1. A car covering a distance of 10km can be treated as a point object.
  2. Earth can be regarded as a point object for studying its motion around the sun.

Question 3.
Give some examples of straight line motion.
Answer:
Examples:

  1. A bus moving on a straight road
  2. A train moving on a straight track
  3. A runner running along a straight track
  4. A ball moving along a straight path
  5. An object falling vertically downwards towards the surface of the earth.

Question 4.
How can we specify the position of an object?
Answer:
1. The position of an object can be specified by choosing:

  • a fixed point called ‘origin’ or reference point, and
  • a fixed line passing through the origin, called reference axis.

2. So the position of an object can be fully described by knowing:

  • its distance from origin O and
  • the angle 0 which the line joining the origin ‘O’ and the object makes with the reference axis.

In the figure shown below, the position of an object located at point P is 6 cm from the origin and 30° north of east. v (Scale: 1cm = 1m)
JAC Class 9th Science Solutions Chapter 8 Motion 18

Question 5.
A body moves in a circle of radius ‘2R’. What is the distance covered and displacement of the body after 2 complete rounds?
Answer:
Distance covered after 2 complete rounds = 2 × circumference
= 2 × 2π (2R) = 8πR
Displacement = zero, because initial and final positions of the body are the same and displacement is the shortest distance between initial and final positions.

Question 6.
Define the term velocity. What is its SI unit? Is it a scalar or a vector quantity?
Answer:
Velocity is a physical quantity that gives both speed and direction of motion of the body.
Definition: Velocity of a body is defined as the displacement produced per unit time. Velocity is also defined as the speed of a body in a givendirection. If ‘s’ is the distance travelled by a body in a given direction and ‘t’ is the time taken to travel that distance, then the velocity V is given by,
Velocity = \(\frac{Displacement}{Time}\)[/latex]
SI unit of velocity is m/s. Velocity is a vector quantity because it requires both magnitude and direction of a body.

Question 7.
Give the difference between distance and displacement.

Distance Displacement
(a) It is the total path covered by an object. (a) It is the shortest path from initial position to the final position.
(b) It does not have any direction. (b) It has direction.
(c) It cannot be zero.V (c) It can be positive, negative or zero.

Question 8.
Differentiate between speed and velocity.
Answer:

Speed Velocity
(a) It is the distance travelled by an object per unit of time. (a) It is the displacement of the body per unit time.
(b) It is a scalar quantity, direction not required. (b) It is a vector quantity, direction is required.
(c) It is always positive. (c) It can be positive, negative or zero.

Question 9.
A cheetah is the fastest land animal and can achieve a peak velocity of 100 km/h upto distances less than 500 m. If a cheetah spots his prey at a distance of 100 m, what is the minimum time it will take to get its prey, if the average velocity attained by it is 90 km/h?
Answer:
Here v = 90Km/h = \(\frac{90 \times 1000 \mathrm{~m}}{3600 \mathrm{~s}}\)
= 25m/s
s = 100m
Minimum time, t = \(\frac{s}{v}\) = \(\frac{100}{25}\) = 4s

Question 10.
The Rajdhani Express travels a distance of 1384 km from Mumbai to Delhi. It starts from Mumbai at 4.00 p.m. and reaches Delhi at 9.00 a.m. the next day. What is its average speed?
Answer:
Total distance travelled = 1384 km
Total time taken = 17 hours
Average speed =\(\frac{Total distance travelled}{Total time taken}\)= \(\frac{1384}{17}\)
= 81.4 km/h

Question 11.
A body starts initially with a velocity ‘u’ and is accelerated at constant rate ‘a’. Find an expression for final velocity after time ‘t’
Answer:
First equation of motion : Let a body start with initial velocity ‘u’ and after time ‘t’, its velocity becomes ‘v’ due to uniform acceleration ‘a’. From the definition of acceleration,
Acceleration = \(\frac{Change in velocity }{Time taken}\)
= \(\frac{Final velocity – Initial velocity}{Time taken}\)
a = \(=\frac{\mathrm{V}-\mathrm{u}}{\mathrm{t}}\)
at = v – u
v = u + at.

Question 12.
Deduce the expression for the distance travelled by a body moving with uniform acceleration in a given time.
Answer:
Second equation of motion:
Suppose a body starts with initial velocity ‘u’ and due to uniform acceleration ‘a’ its final velocity becomes ‘v’ after time ‘t’ Then,
Average velocity = \(\frac{Initial velocity + Final velocity}{2}\)
=\(\frac{u+v}{2}\)
So, the distance covered by the body in time t is
s = Average velocity × Time =\(\frac{u+v}{2}\) × t = \(\frac{\mathrm{u}+(\mathrm{u}+\mathrm{at}) \times \mathrm{t}}{2}\)
= \(\frac{2 u t + a t^{2}}{2}\)
or s = ut + \(\frac{1}{2}\) at 2

JAC Class 9 Science Important Questions Chapter 8 Motion

Question 13.
Establish the relation v2 – u2 = 2as, where ‘u’ is the initial velocity, ‘v’ is the final velocity, ‘a’ is the uniform acceleration and ‘s’ is the distance covered by the body.
Answer:
Third equation of motion:
Let a body start with initial velocity ‘u’ and after covering distance ‘s’ under uniform acceleration ‘a’, its velocity becomes ‘v’ in ‘t’ seconds. Then
Average velocity = \(\frac{\mathrm{u}+\mathrm{v}}{2 \mathrm{}}\)
So the distance covered in time t is given by
s = Average velocity x Time
= \(\frac{u+v}{2}\) × t
or v + u = \(\frac{2 s}{t}\) …………..(1)

Using the first equation of motion: v = u + at
or v – u = at … (ii)

Multiplying equations (i) and (ii), we get
(v + u) (v – u) = \(2 \frac{s}{t}\) × at
or v2 – u2 = 2as

Question 14.
Show that the slope of distance – time graph gives velocity of the body.
JAC Class 9th Science Solutions Chapter 8 Motion 19
Answer:
Given figure shows distance – time graph for a body moving with uniform velocity. Clearly, it covers distances s1 and s2 in times t1 and t2 respectively.
Slope of line AB = tan θ = \(\frac{\mathrm{BC}}{\mathrm{AC}}\)
= \(\frac{s_{2}-s_{1}}{t_{2}-t_{1}}\) = \(\frac{Displacement}{Time}\) = velocity
Hence, the slope of the distance-time graph gives velocity of the body.

Question 15.
Show that the slope of velocity time graph gives acceleration of the body.
Answer:
Given figure shows the velocity – time graph for a body in uniform acceleration. It is a straight line inclined to the time – axis. Body has velocities ‘u’ and ‘v’ at times ‘t1’ and ‘t2’ respectively
Img-1
Slope of line AE = tan θ = \( \frac{E D}{A D}\)
\(\frac{v-u}{t_{2}-t_{1}}\) = \( \frac{Change in velocity}{Time taken}\)
= Acceleration of the body
Hence, the slope of the velocity – time graph gives the acceleration of the body.

Question 16.
Draw velocity – time graph for a body moving with uniform velocity. Hence show that the area under the velocity time graph gives the distance travelled by the body in a given time interval.
Answer:
In the given figure, line PQ is the velocity – time graph of a body moving with a uniform velocity such that OP = v Area of rectangle ABCD = AD × AB
= OP × AB
= v × (t2 – t1)
= Velocity × Time
= Distance travelled in time interval (t2 – t1)
JAC Class 9th Science Solutions Chapter 8 Motion 20
Hence, the area under the velocity – time graph gives the distance travelled by the body in the given time interval.

Question 17.
The odometer of a car reads 1800 km at the start of a trip and 2400 km at the end of the trip. If the trip took 10h, calculate the average speed of the car in km/h and m/s.
Answer:
Distance covered by the car (s)
= 2400 – 1800 = 600 km.
Trip time = 10h
Average speed = ?

(i) Vav = \(\frac{s}{t}\) = \(\frac{600}{10}\) km = 60 km/h

(ii) In m/s : (60 km/h) = \(\frac{60 \times 1000}{60 \times 60}\)
= 16.7 m/s
The average speed of the car in km/h is 60 km/h and in m/s is 16.7 m/s.

Question 18.
Draw velocity – time graphs to show the following:
(a) Uniform velocity
(b) Uniform acceleration
(c) Non – uniform acceleration
Answer:
JAC Class 9th Science Solutions Chapter 8 Motion 21
JAC Class 9th Science Solutions Chapter 8 Motion 22

Analysing & Evaluating Questions

Question 19.
The table given below shows distance (in km) travelled by bodies A, B and C. Read the data carefully and answer the following questions.

Distance (in km) covered by different bodies
Time (s) Body(A) Body (B) Body (C)
1st second 20 20 20
2nd second 20 36 60
3rd second 20 24 100
4th second 20 30 140
5 th second 20 48 180

(a) Which of the bodies is moving with
(i) constant speed?
(ii) constant acceleration?
(b) Which of the bodies covers
(i) maximum distance in 3rd second?
(ii) minimum distance in 3rd second?
Answer:
(a) (i) Body A
(ii) Body C

(b) (i) Body C
(ii) Body A

Question 20.
An electron moving with a velocity of 5 × 104ms-1 enters a uniform electric field and acquires a uniform acceleration of 104ms-2 in the direction of its initial motion.
(a) Calculate the time in which the electron would acquire a velocity double of its initial velocity.
(b) How much distance the electron would cover in this time?
Answer:
(i) Acceleration = \(\frac{ Change in velocity}{Time taken}\)
or Time taken, t = \(\frac{5 \times 10^{4} \mathrm{~m} \mathrm{~s}^{-1}}{10^{4} \mathrm{~m} \mathrm{~s}^{-2}}\)
= 5 s

(ii) s = ut + \(\frac{1}{2}\) at2
= (5 × 104 m s-1 × 5 s) + \(\frac{1}{2}\) × 104m s-2 × (5s)2
= 37.5 × 104 m

Long Answer Type Questions

Question 1.
Describe the various types of motion observed in bodies.
Answer:
Various types of motion as observed in bodies are:

  1. Translatory motion: When a body moves, as a whole, along a straight or curved path, it is said to be in translatory motion. Translatory motion is again of two types:
    • Rectilinear motion : Here a body moves as a whole along a straight path. For example, a train moving on a straight track has translatory rectilinear motion.
    • Curvilinear motion : In this case a body moves as a whole along a curved path. For example, motion of a bicycle taking a turn along a curved path.
  2. Rotatory motion: When a body rotates about a fixed point or axis. it exhibits a rotatory motion. For example, motion of a flywheel about a shaft
  3. Vibratory or oscillatory motion: When a body moves to and fro about a mean position, the motion is said to be vibratory or oscillatory motion. For example, the motion of the pendulum of a wall – clock.
  4. Complex motion: When the motion of a body may be a combination of more than one type of motion, it is said to be a complex motion. For example, a ball rolling down an inclined plane has both translatory and rotatory motions.

Question 2.
Define average velocity when the velocity of a body changes at a non – uniform rate and a uniform rate.
Answer:
Average velocity : When the velocity of a body changes at a non – uniform rate, its average velocity is defined as the net displacement covered divided by the total time taken.
Average velocity = \(\frac{Net displacement}{Total time taken}\)
When the velocity of a body changes at a uniform rate, the average velocity is given by the arithmetic mean of initial velocity and final velocity for a given period of time.
Average velocity = \(\frac{Initial velocity + Final velocity}{2}\) :
If u is the initial velocity and v is the final velocity, the average velocity vay is given by,
vay = \(=\frac{u+v}{2}\)

Question 3.
Explain the difference regarding the nature of acceleration of the three moving bodies as expressed by the following velocity – time graphs:
JAC Class 9th Science Solutions Chapter 8 Motion 23
(a) Uniform acceleration: A body increases velocity by equal amounts in equal intervals of time.
(b) Non – uniform acceleration: A body travels unequal distances in equal intervals of time.
(c) Uniform motion or zero acceleration: A body moves with constant

Analysing & Evaluating Questions

Question 4.
Two stones are thrown vertically upwards simultaneously with their initial velocities u1 and u2 respectively. Prove that the heights reached by them would be in the ratio of \(\mathbf{u}_{1}^{2}\) : \(\mathbf{u}_{2}^{2}\) (Assume upward acceleration is – g and downward acceleration to be + g).
Answer:
Stone 1
Initial velocity = u1
Acceleration = – g
Height = h,
Final velocity, v = 0
Using the equation, v2 – u2 =2as
0 – \(\vec{a}\) = 2 (- g) × h1
h1 = \(\frac{-u_{1}^{2}}{-2 g}\) = \(\frac{u_{1}^{2}}{2 g}\) ……..(1)

Stone 2
Initial velocity = u1
Acceleration = – g
Height = h2
Final velocity, v = 0
02 \(-u_{2}^{2}\) = 2 (- g) × h2
h2 = \(\frac{-u_{2}^{2}}{-2 g}\) =\(\frac{u_{2}^{2}}{2 g}\) ……..(ii)
This gives; h1 : h2 = \(\vec{a}\) : \(\vec{a}\)
= \(=\frac{u_{1}^{2}}{2 g}\) : \(\frac{\mathrm{u}_{2}^{2}}{2 \mathrm{~g}}\)
=\(u_{1}^{2}\) : \(\vec{a}\)

Activity 1

  1. In your everyday life, you come across a range of motions in which:
    • acceleration is in the direction of motion
    • acceleration is against the direction of motion
    • acceleration is uniform
    • acceleration is non – uniform
  2. Observe these motions carefully and identify one example each of the above type of motions.

Observations

  • A car moving on a road.
  • A ball thrown up.
  • Fan blades rotating
  • Windmill at time moves fast when the wind speed is more and becomes slow when the wind speed decreases.

Activity 2

  • Take piece of thread and tie a small piece of stone at one of its end. Move the stone to describe a circular path with constant speed by holding the thread at the other end.
    JAC Class 9th Science Solutions Chapter 8 Motion 24
  • Now, let the stone go by releasing the thread.
  • Observe the direction in which the stone moves after it is released.
  • By repeating the activity for a few more times and releasing the stone at different positions of the circular path, carefully observe whether the direction in which the stone moves remains the same or not.

Observations

  • When the stone is released, it moves along a straight line, tangential to the circular path.
  • By repeating the activity and releasing the stone at different positions of the circular path, the direction in which the stone moves does not remain the same. It changes every time.

Value Based Questions

Question 1.
The speed limits are prescribed for vehicles running on highways. Why is it essential to follow the speed limit rules?
Answer:
Speed limits are prescribed on the highways/expressways because:
1. When a vehicle is made to run at height speeds, its tyres get hot (due to friction). This makes them softer and the air inside the tubes hotter Both. these factors may lead to bursting of tyre/tube.

2. Reflex time varies from person to person. Any running vehicle needs a certain time period to stop after the brakes are applied. At higher speeds, this time period becomes shorter.

3. As a result, the chances of collision increase. Because of these reasons, one should strictly follow the speed limit regulations. Also, it is safer to drive in your lane depending upon the speed of your vehicle.

4. Moral: Drive below the speed limit and in your lane.

Question 2.
Most drivers involved in road accidents are found to be drunk. Give reason.
Answer:
The reflex time of a person increases when drunk, (average reflex time of a normal person is about 1/15s). Therefore, such a driver of vehicle will take more time in applying brakes. As a result, the vehicle may not stop well in time and cause an accident.

JAC Class 9 Science Important Questions

JAC Class 9 Science Important Questions Chapter 7 Diversity in Living Organisms

JAC Board Class 9th Science Important Questions Chapter 7 Diversity in Living Organisms

Multiple Choice Questions

Question 1.
Whittaker classified all organisms into
(a) five kingdoms
(b) four kingdoms
(c) three kingdoms
(d) two kingdoms
Answer:
(a) five kingdoms

Question 2.
A housefly belongs to which phylum?
(a) Nematoda
(b) Annelida
(c) Porifera
(d) Arthropoda
Answer:
(d) Arthropoda

Question 3.
The five kingdom classification is based on the complexity of
(a) mode of nutrition
(b) body organisation
(c) cell structure
(d) all of these
Answer:
(d) Arthropoda

Question 4.
Which one of the following belongs to coelenterata?
(a) Sycon
(b) Hydra
(c) Spongilla
(d) Planaria
Answer:
(b) Hydra

Question 5.
In which of the following are the reproductive organs hidden?
(a) Cryptogamae
(b) Phanerogamae
(c) Gymnosperms
(d) Angiosperms
Answer:
(a) Cryptogamae

Question 6.
Which phylum of animals is also called flatworms?
(a) Porifera
(b) Coelenterata
(c) Platyhelminthes
(d) Nematoda
Answer:
(c) Platyhelminthes

Question 7.
The excretory system in annelids consists of tubes called
(a) flame cells
(b) metanephridia
(c) nephridia
(d) protonephridia
Answer:
(c) nephridia

Question 8.
What is the phylum of octopus?
(a) Arthropoda
(b) Mollusca
(c) Annelida
(d) Cnidaria
Answer:
(b) Mollusca

JAC Class 9 Science Important Questions Chapter 7 Diversity in Living Organisms

Question 9.
What is the mode of nutrition in bacteria?
(a) Autotrophic
(b) Heterotrophic
(c) Both (a) and (b)
(d) None of these
Answer:
(c) Both (a) and (b)

Question 10.
In which organism do flame cells form the excretory system?
(a) Flatworm
(b) Earthworm
(c) Insect
(d) Crab
Answer:
(a) Flatworm

Question 11.
Which sub – group in plant kingdom produces flowers?
(a) Angiosperm
(b) Fungus
(c) Moss
(d) Fern
Answer:
(a) Angiosperm

Question 12.
The mode of nutrition in fungi is
(a) only saprotrophic
(b) saprotrophic or parasitic
(c) only parasitic
(d) none of the above
Answer:
(b) saprotrophic or parasitic

Question 13.
Which among the following is exclusively marine?
(a) Arthropoda
(b) Mollusca
(c) Echinodermata
(d) Coelenterata
Answer:
(c) Echinodermata

Analysing & Evaluating Questions

Question 14.
Meena and Hari observed an animal in their garden. Hari called it an insect, while Meena said it was an earthworm. Which of the following characteristics confirms that it was an insect?
(a) Bilaterally symmetrical body
(b) Body with jointed legs
(c) Cylindrical body
(d) Body with little segmentation
Answer:
(b) Body with jointed legs

Question 15.
After studying the characteristics of Agaric us, Madan noted them as follows:
I. It is fleshy.
II. It has an umbrella-like cap called pileus.
III. Spores are produced by the stipe.
IV. Its body is made of filaments.
Which observation is not correct?
(a) I
(b) II
(c) III
(d) IV
Answer:
(c) III

Question 16.
Preeti studied the following
features in a preserved specimen – bilateral symmetry, true segmentation, clitellum and mouth. It is a/an
(a) tapeworm
(b) cockroach
(c) earthworm
(d) roundworm
Answer:
(c) earthworm

Assertion Reason Questions

Directions: In the following questions, the Assertions and the Reasons have been put forward Read the statements carefully and choose the correct alternative from the following:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.
(C) The assertion is true but the reason is false.
(D) Both the statements are false.

1. Assertion: Bacteria and blue – green algae belong to the same phylum, i.e. Monera.
Reason: Both the bacteria and blue – green algae are unicellular prokaryotic organisms.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

2. Assertion: Most of the amphibians lay their eggs in water.
Reason: Young ones of amphibians have gills at the initial stages of there lives.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

3. Assertion: Snake and turtle belong to the same group.
Reason: Both the snake and the turtle are cold – blooded and have four – chambered heart.
Answer:
(C) The assertion is true but the reason is false.

4. Assertion: Dolphins do not belong to pisces.
Reason: Dolphins respire through lungs and possess four – chambered heart.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

5. Assertion: Roundworms lack a digestive tract.
Reason: Roundworms are endoparsites.
Answer:
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.

Very Short Answer Type Questions

Question 1.
What is evolution?
Answer:
Evolution is the gradual unfolding of organisms, from the pre – existing ones, through changes since the beginning of life.

Question 2.
Name the scientist who described the idea of organic evolution and the book in which he explained it.
Answer:
Charles Darwin first described the idea of evolution in his book ‘The Origin of Species’.

JAC Class 9 Science Important Questions Chapter 7 Diversity in Living Organisms

Question 3.
What is lichen?
Answer:
Lichens are a complex life form that is a symbiotic partnership of two separate organisms, i.e., a fungus and an alga The alga can be either a green alga or a blue-green alga (also known as cyanobacteria).

Question 4.
What is a symbiotic relationship or symbiosis?
Answer:
It is a relationship between two organisms in which both of them are benefited, e.g., in the symbiotic association of lichens, fungi get food from blue – green algae and in return, blue-green algae get shelter.

Question 5.
Who proposed the two kingdom classification?
Answer:
Carolus Linnaeus.

Question 6.
What is biodiversity?
Answer:
Different forms of living organisms found in a particular region is known as biodiversity of that region.

Question 7.
Define species.
Answer:
A species includes all organisms that are similar enough to interbreed and perpetuate naturally.

Question 8.
Define mycoplasma.
Answer:
Mycoplasma are the smallest and the simplest organisms. They are prokaryotes having a nucleoi(d) Their body can change shape easily. They are heterotrophs.

Question 9.
Define ‘taxonomy’.
Answer:
The branch of science that classifies living organisms among different categories or groups is called taxonomy. Taxonomy is the science of identifying and naming species and organising them into systems of classification.

Question 10.
Define Taxon.
Answer:
A taxon is a unit of classification of organisms which can be recognised to a definite category at any level of classification, for e.g., fishes, birds, insects, etc.

Question 11.
In how many kingdoms does Carolus Linnaeus divided living beings?
Answer:
Two kingdoms, viz., Plantae (plants) and Animalia (animals).

Question 12.
Name the division of plant kingdom which is also called the amphibians of plant kingdom.
Answer:
Bryophyta, e.g., Lunaria (moss).

Question 13.
What is meant by bilateral symmetry?
Answer:
When the left and right halves of the body have the same design, it is called bilateral symmetry.

Question 14.
What is thallus?
Answer:
Thallophytes have a simple plant body. The plant body is not differentiated into root, stem and leaves and is called thallus.

Question 15.
What is moss?
Answer:
Moss is a radially symmetrical leafy bryophyte having multicellular rhizoids, Funaria, Bryum, Sphagnum.

Question 16.
Why are bryophytes called the amphibians of the plant kingdom?
Answer:
Bryophytes are known as amphibians of the plant kingdom because these plants can live in soil but are dependent on water for sexual reproduction. Usually, they are found in humid and damp areas.

Analysing & Evaluating Questions

Question 17.
The external features of some living organisms are given below as I, II, III and IV. Read these and write the name of their respective animal phylum or class.
I. Streamlined body, covered with scales and divided externally into head, trunk and tail.
II. Skin is dry, covered with epidermal scales and bear two pairs of limbs each with five toes ending in horny claws.
III. Body is externally segmented and covered with a thick exoskeleton made up of chitin. The segments are grouped to form head, thorax and abdomen.
IV. Body is flattened, leaf-like or ribbon – like and bilaterally symmetrical.
Answer:
I – Phylum chordata (superclass pisces)
II – Phylum chordata (class reptilia)
III – Phylum arthropoda
IV – Phylum platyhelminthes

Question 18.
An animal is described as worm-like with unsegmented body and shows some features of  invertebrates and some of chordates. Identify the described animal.
Answer:
The animal is Balanoglossus.

Question 19.
Atrip to Himalayan foothills was organised by the school of Raman and Riya During the trip, they noticed tall trees having needle – like leaves and cones. Name the trees Raman and Riya saw there.
Answer:
They saw Pinus trees.

Short Answer Type Questions

Question 1.
What are the steps in classification of organisms?
Answer:
Organisms are classified into large groups first on the basis of independent characteristics. The characteristic in the next level would be dependent on the previous one and would decide the variety of organisms in the next level. Thus, one can build up a whole hierarchy of mutually related characteristics to be used for classification.

Question 2.
Write the hierarchy of classification proposed by Linnaeus.
Answer:
The hierarchical categories are as follows:

  • Kingdom: Plant kingdom and Animal kingdom.
  • Phylum (for animals)Division (for plants): A group of closely related classes having certain common characteristics.
  • Class: A group of closely related orders having certain common characteristics.
  • Order: A group of closely related families having certain common characteristics.
  • Family: A group of closely related genera having certain common characteristics.
  • Genus: A group of closely related species having certain common characteristics.
  • Species: A group of organisms which are similar enough to breed and perpetuate.

Question 3.
What are the characteristics of kingdom Monera?
Answer:

  1. These organisms do not have clearly defined nucleus, i.e., nucleus is not enclosed in a nuclear membrane.
  2. Cell organelles are not covered with membranes.
  3. The organisms do not show multicellular body design, i.e., they are unicellular.
  4. Some organisms have cell wall, others do not have cell wall.
  5. The mode of nutrition may be autotrophic or heterotrophic.

Question 4.
Why are blue green algae included under Monera and not under Plantae?
Answer:
Monera is a kingdom of prokaryotes while organisms of kingdom Plantae shows a definite nucleus, membrane- bound organelles and multicellular body design. Blue green algae are prokaryotes having nucleoid with naked DNA. The cell organelles are also not enclosed within a membrane. As they also do not possess multicellular body design, these characteristics bring them closer to Monera and exclude them from the kingdom Plantae.

Question 5.
Give four main features of organisms placed under Protista.
Answer:
The four main features of organisms placed under Protista are as follows:

  1. This kingdom includes unicellular algae, diatoms and protozoans.
  2. The organisms in this kingdom are unicellular, eukaryotic organisms (as well – defined nucleus and other membrane-bound cell organelles are present).
  3. Mode of nutrition is either autotrophic (like in algae and diatoms) or heterotrophic (like in protozoans).
  4. Some Protists bear hair – like cilia or whip – like flagella for movement. In some protists, like Amoeba, movement takes place by pseudopodia (false feet).

JAC Class 9 Science Important Questions Chapter 7 Diversity in Living Organisms

Question 6.
What are the characteristics of fungi? Give examples.
Answer:
Characteristics of fungi are as follows:

  1. They are heterotrophic.
  2. The organisms are saprophytic, i.e., they use decaying organic material as food or may be parasitic.
  3. They have membrane bound nucleus.
  4. They have cell walls made of chitin.
  5. Some of them have the capacity to become multicellular organisms at certain stages in their lives.
  6. Some of the fungal species have symbiotic relationship where they are mutually dependent on the blue – green algae. These are called lichens.
  7. Examples: Rhizopus, Yeast, Agaricus (mushrooms), Penicillium.

Question 7.
On what basis are plants divided into two sub-kingdoms?
Answer:
Based on whether the reproductive organs are conspicuous (clearly visible) or not, plants are divided into two subkingdoms:

  1. Cryptogamae: Non – flowering or seedless plants which include thallophytes, bryophytes and pteridophytes.
  2. Phanerogamae: Flowering plants which include gymnosperms and angiosperms.

Question 8.
How are angiosperms further divided?
Answer:
Angiosperms are divided into two groups on the basis of the number of cotyledons present in the seeds.

  1. Monocotyledonous (Monocots): These are the plants with seeds having a single cotyledon, e.g., maize, wheat, rice, etc.
  2. Dicotyledonous (Dicots): These are the plants with seeds having two cotyledons, e.g., pea, gram, bean, etc.

Question 9.
List the similarities between plants and animals.
Answer:
In spite of certain external differences, plants and animals show a number of very obvious similarities which are as follows:

  1. Plants and animals are made up of microscopic units called cell.
  2. Both contain living substance called protoplasm.
  3. Certain life processes, i.e., respiration, digestion, reproduction, assimilation, etc., take place in both the groups in an identical manner.
  4. Both show response to external stimuli.
  5. Both of them show growth.
  6. Both reproduce and pass on their hereditary characters to their offsprings by the same mechanism.
  7. Both are multicellular and eukaryotic organisms having division of labour in their cells.

Question 10.
Differentiate between algae and fungi.
Answer:

Algae Fungi
(a) Contain chlorophyll (green in colour). (a) Do not contain chlorophyll (nongreen).
(b) Autotrophic nutrition. (b) Heterotrophic nutrition.
(c) Food is stored in the form of starch. (c) Food is stored in the form of glycogen.
(d) The cell wall is made up of cellulose. (d) The cell wall is made up of chitin.
(e) Example: Spirogyra. (e) Example: Rhizopus (bread mould)

Question 11.
What are the conventions followed for writing the scientific names?
Answer:
The conventions followed while writing the scientific names are as follows:

  1. The name of the genus begins with a capital letter.
  2. The name of the species begins with a small letter.
  3. When printed, the scientific name is given in italics.
  4. If it is handwritten, the genus name and the species name have to be underlined separately.

Question 12.
Identify the different parts A, B, C and D of fern plant shown in the figure given below.
JAC Class 9th Science Solutions Chapter 7 Diversity in Living Organisms 1
Answer:
(A) Leaflet
(B) Stipe
(C) Adventitious roots
(D) Rhizome

Question 13.
Define bryophytes. Give some examples.
Answer:

  1. Bryophytes:
    • These are also called the amphibians of the plant kingdom.
    • Plant body may be thalloid or leafy.
    • True roots are absent, instead rhizoids develop.
    • No specialised conducting tissue. These grow on damp walls and on the bark of tree.
  2. These include two groups:
    • Liverworts
    • Mosses
  3. Examples: Marchantia, Riccia, Sphagnum, etc.

Question 14.
Draw a labelled diagram of Spirogyra cell.
Answer:
JAC Class 9th Science Solutions Chapter 7 Diversity in Living Organisms 2

Question 15.
Define pteridophytes.
Answer:
Pteridophytes are vascular cryptogams and are the first vascular land plants. The main plant body is the saprophyte, which is differentiated into true roots, stems and leaves. Their xylem lacks companion cells. They have specialised tissue for the conduction of water and other substances from one part of the plant body to another. Examples: Mars ilea, ferns and horse tail.

Question 16.
Define coelom.
Answer:
Coelom is a cavity which lies in between the body wall and gut (alimentary canal) and is lined by mesodermal cells. It allows greater body flexibility. In it, the organs of the body can accommodate in a better way.

Question 17.
Differentiate between diploblastic and triploblastic animals.
Answer:

Diploblastic Triploblastic
The animals whose bodies are developed from two layers of gastrula, i.e., ectoderm and endoderm, are called diploblastic For example, coelenterates (Hydra). The animals whose bodies develop from three layers of gastrula, i.e., ectoderm, mesoderm and endoderm, are called triploblastic, e.g., tapeworm.

Question 18.
State the features of chordates.
Answer:
The main features of chordates are as follows:

  1. They have bilaterally symmetrical body.
  2. They have notochord and internal skeleton.
  3. They have dorsal nerve cord.
  4. They are triploblastic.
  5. They are coelomate.
  6. Respiration is mainly through lungs in land vertebrates and by gills in aquatic animals.

Question 19.
Discuss the characteristics of sponges.
Answer:
Phylum (Porifera) – Sponges:

  1. Animals have pores (called ostia) all over the body.
  2. Body is not well differentiated.
  3. Non – motile animals, remain attached to solid support.
  4. Body is covered with hard skeleton.
  5. Reproduction is both asexual (by budding and gemmule formation) and sexual (through fertilisation).
  6. Examples: Sycon, Spongilla and Euplectella.

Question 20.
Give specific features of coelenterata.
Answer:
Phylum (Cnidaria) – Coelenterata

  1. All coelenterates are found in water.
  2. Body is radially symmetrical.
  3. These are the first of multicellular animals which possess tissue level of organisation with a distinct division of labour.
  4. The body has a single, sac – like central cavity, called coelenteron or the gastrovascular cavity, with only one opening.
  5. Some coelenterates live in colonies (Obelia) while others live solitary (Hydra).
  6. Examples: Hydra, Aurelia, sea anemone and jelly fish.

JAC Class 9 Science Important Questions Chapter 7 Diversity in Living Organisms

Question 21.
Give the general characteristics of Platyhelminthes.
Answer:

  1. Their body is dorsoventrally flattened and leaf-like or ribbon like.
  2. Body symmetry is bilateral, i.e., left and right halves have the same design.
  3. They are mostly hermaphrodite.
  4. Body cavity or true coelom is absent.
  5. There are three layers of cells from which differentiated tissues can be forme(d) So, animals are triploblastic.
  6. They are either free living or parasitic.
  7. Examples: Planaria, Fasciola hepatica (liver fluke) and Taenia solium (tape worm) are parasitic.

Question 22.
Give the characteristics of Arthropoda with two examples.
Answer:

  1. This is the largest group of animals.
  2. They possess jointed legs/ appendages.
  3. They have bilaterally symmetrical and segmented body.
  4. Body cavity is filled with blood.
  5. There is an open circulatory system, i.e., the blood does not flow in definite blood vessels.
  6. Examples: Apis (honey bee), Musca (housefly), Anopheles (mosquito), Palaemon (prawn), crabs, etc

Question 23.
Give the characteristics of Echinoder – mata.

  1. They are free living, marine animals.
  2. They are triploblastic and have a coelomic cavity.
  3. They have peculiar water-driven tube system used for moving around.
  4. They have a hard calcium carbonate structure that is used as skeleton.
  5. Sexes are separate.
  6. Examples: Asterias (starfish),

Question 24.
Echinus (sea urchin), Antedon (feather star), etc Give the characteristics of Nematoda.

  1. Most of the Nematodes have small cylindrical or round body.
  2. Body cavity is not a true coelom. A pseudocoelom is present.
  3. Body is bilaterally symmetrical and triploblastic.
  4. Sexes are separate.
  5. Examples: Ascaris (round worm), Ancylostoma (hook worm) and Wuchereria (filarial worm).

Question 25.
Give the characteristics of phylum Annelida.

  1. They have elongated and segmented body.
  2. Body bears lateral appendages for locomotion in the form of chitinous setae or parapodia.
  3. The body is bilaterally symmetrical and triploblastic.
  4. Reproduction by sexual means. Sexes may be either separate or united.
  5. They have true coelom (body cavity).
  6. Examples: Pheretima (earthworm), Hirudinaria (blood sucking leech) and Nereis.

Question 26.
List the main features of phylum Mollusca.
Answer:

  1. They have unsegmented or soft body with little segmentation.
  2. The body is divided into three regions—head, dorsal visceral mass and ventral foot.
  3. Body is bilaterally symmetrical.
  4. The coelomic cavity is reduced.
  5. They have open circulatory system and kidney-like organs for excretion.
  6. Some molluscs have hard calcareous shell, an outer covering of the body.
  7. Respiration is by gills called ctenidia.
  8. Examples: Pila (snail), Unio (fresh water mussel) and Octopus.

Analysing & Evaluating Questions

Question 27.
You are given leech, Nereis, Scolopendra, prawn and scorpion and all have segmented body organisation. Will you classify them in one group? If no, give the important characteristics based on which you will separate these organisms into different groups.
Answer:
Leech, Nereis, Scolopendra, prawn and scorpion belong to different groups.

  1. Leech and Nereis belong to phylum Annelida They have metameric segmentation, closed circulatory system and unjointed appendages.
  2. Scolopendra, prawn and scorpion belong to phylum Arthropoda They have open circulatory system and jointed appendages.

Question 28.
Sakshi’s younger brother frequently suffered from stomach ache and vomiting. Her mother took him to a clinic for treatment. Doctor advised for a stool test before prescribing some medicines. The report diagnosed that the stool is infected with common roundworms. Answer the following questions asked by Sakshi to the doctor:
(a) What are common roundworms?
(b) Are there any other worms that live as parasites in our body and cause diseases?
(c) How do roundworms enter our body? What can be done to prevent such infections?
Answer:

  1. Common roundworms are parasites that live inside the human digestive tract and feed on the food present inside the tract. During feeding, they damage the stomach and the intestines. The scientific name of roundworms is Ascaris.
  2. Some other common parasitic worms that cause different diseases in our body are Wuchereria (filarial worm), Enterobius (pinworm) and Ancylostoma (hookworm).
  3. Roundworms enter our body through contaminated food and water. Hence, one should always maintain hygienic food habits to avoid these parasites.

Long Answer Type Questions

Question 1.
Describe the three basic features for grouping all organisms into five major kingdoms.
Answer:
Basic criteria such as nature of cell, cellularity and mode of nutrition were used by Whittaker to classify the living organisms into five kingdoms,
(a) Nature of cell relates to the pres – ence or absence of membrane bound organelles in it. On the basis of this category, we can clas¬sify the living organisms in two broad categories prokaryotes and eukaryotes.

  1. Prokaryotes, such as all bacteria, have poorly developed nuclear material called nucleoid and no membrane – bound organelles.
  2. Eukaryotes such as protozoans, fungi, plants and animals have well developed genetic material called nucleus and all membrane – bound organelles.

(b) Cellularity refers to the number of cells present in an organism. Unicellular organisms, such as bacteria, and protozoans, are made up of single cell while multicellular organisms such as many fungi, plants and animals are made up of many cells.

(c) Mode of nutrition categorises all living organisms into autotrophs and heterotrophs. Euglena is a dual organism because of its mode of nutrition. It can act as both an autotroph (makes its own food) as it contains chlorophyll and heterotroph (feeds on other substances). Also, in presence of excess organic matter or darkness, it can act as a saprophytic organism. So, as it shows features of both plants and animals, it is a dual organism.

Question 2.
Give the outline classification of animal kingdom upto the level of phyla
JAC Class 9th Science Solutions Chapter 7 Diversity in Living Organisms 3

Question 3.
What are the differences between plants and animals?
Answer:

Animals Animals
(a) Most of the plants around us are stationary and do not move from one place to another. (A) Most of the animals around us are mobile, i.e., they can move from one place to another.
(b) Plants can synthesise their own food in the presence of sunlight from water and carbon dioxide. In their green parts like leaves,chlorophyll pigment is found which helps in food making by the process of photosynthesis. (b) Animals cannot synthesise their food because they lack chlorophyll. So, they directly or indirectly depend on plants.
(c) Most of the plants continue growing throughout their life. The growth may be in length (height) or producing lateral branches. (c) Animals stop growing, especially in length, (height) after attaining a certain maturity.
(d) Plant cells have cell walls as outermost covering. (d) Animal cells do not have cell walls.

Question 4.
Differentiate between bryophytes and pteridophytes.
Answer:

Bryophytes Pteridophytes
(a) Plant body is either leafy or thalloid. (a) Plant body is differentiated into roots, stem and leaves.
(b) The cells in plant body are haploid. (b) The cells in plant body are diploid.
(c) Vascular tissue like xylem and phloem is absent. (c) Vascular tissue like xylem and phloem is present.
(d) In life cycle, the gametophyte is dominant. (d) In life cycle, the sporophytes are dominant.
(e) Sporophytic phase completely depends upon gametophytes. (e) Sporophytic phase is independent and autotrophic.
(f) The spores are produced in the capsule part of the sporophytes. (f) The spores are produced in sporangia bom on the leaves called sporophylls.
(g) Example: Moss. (g) Example: Fem.

Question 5.
Give the classification of plant kingdom.
JAC Class 9th Science Solutions Chapter 7 Diversity in Living Organisms 4

Question 6.
Write the characteristics of flat worms, round worms and segmented worms. Write their phylum also.
Answer:

Flat worms Round worms Segmented worms
1. Phylum – Platyhelminthes. 1. Phylum – Nematoda 1. Phylum – Annelida.
2. Dorsoventrally flat, i.e., flat body. 2. Body is cylindrical. 2. Body is segmented from head to tail.
3. No true body cavity (acoelomates). 3. Pseudocoelom (false body cavity). 3. True body cavity (eucoelomates).
4. Mostly hermaphrodite, i.e., male and female sex organs present in the same individual. 4. Sexes are separate. 4. May be unisexual or bisexual.


Analysing & Evaluating Questions

Question 7.
Observe the plant given below and answer the questions that follow.
1. Identify the plant and name the phylum it belongs to.
2. What is its habitat?
3. List any two of its special features.
4. How does transport of substances take place in this plant?
Answer:

  1. It is a Cycas plant. It belongs to the phylum gymmosperms.
  2. It is found mainly in colder regions of the earth.
    JAC Class 9th Science Solutions Chapter 7 Diversity in Living Organisms 5
  3. Plant body is sporophyte. Ovules are not enclosed in ovary, thus produce naked seeds.
  4. Vascular tissues are present for the conduction of substances.

Activity 1

Find out the scientific names of the following animals and plants:
(a) Frog
(b) Peacock
(c) Human
(d) Neem
(e) Maize
(f) Honeybee

Observations
It is difficult to remember names of a species in different languages. There was a need for some system to create uniform naming convention.

Animal/Plant Scientific Name
1. Frog 1. Rana tigrina
2. Peacock 2. Pavo cristatus
3. Human 3. Homo sapiens
4. Honeybee 4. Apis indica
5. Neem 5. Azadirachta indica
6. Maize 6. Zea mays

 

Activity 2

  • Soak seeds of green gram, wheat, maize, pea and tamarin(d) Once they become tender, try to split the seeds. Observe if the seeds break into two nearly equal halves.
  • Now, observe the roots, leaves and flowers of these plants and record your observations.
    Observations
  • All seeds do not break into two nearly equal halves.
  • Out of the given seeds, gram, pea and tamarind are dicots while wheat and maize are monocots.
  • Dicot plants have tap-roots and monocots have fibrous root system.
  • Dicot plant leaves have reticulate venation, whereas monocot leaves have parallel venation.
  • In monocot flowers, petals are three or in multiples of three (trimerous). In dicot flowers, petals are five or in multiples of five (pentamerous).

Value Based Questions

Question 1.
Many medicinal plants are getting extinct every year. A group of students who had gone for educational trip clicked photographs of endangered plants. These photographs were used by the school laboratory to study these plants.
1. Name two endangered plants.
2. Name any one medicinal plant and write its medicinal use.
3. What value of students is reflected in the above act?
Answer:

  1. Two endangered plants are: Lotus comiculatus and Acacia planifrons.
  2. Aloe – vera Juice of Aloe vera is used in case of indigestion, treating skin infections, etc.
  3. Students are caring citizens, showing responsible behavior.

Question 2.
Due to global warming, coral is getting diminished in all the oceans/water bodies. People in the Lakshadweep island protect their corals by not allowing people/tourists to take few pieces away.
1. Name the phylum of coral.
2. What is coral made up of?
3. What values of people in Lakshadweep island are reflected?
Answer:

  1. Phylum of coral is coelenterata.
  2. Coral is made up of calcium carbonate.
  3. People in Lakshadweep island reflect the values of being responsible citizens, respecting environment and nature.

JAC Class 9 Science Important Questions

JAC Class 9 Science Important Questions Chapter 6 Tissues

JAC Board Class 9th Science Important Questions Chapter 6 Tissues

Multiple Choice Questions

Question 1.
Which are the two types of tissues?
(a) Meristematic and temporary
(b) Meristematic and permanent
(c) Meristems and temporary
(d) None of these
Answer:
(b) Meristematic and permanent

Question 2.
Parenchyma is a type of
(a) complex tissue
(b) simple tissue
(c) xylem
(d) phloem
Answer:
(b) simple tissue

Question 3.
Transpiration and exchange of gases are functions of
(a) stomata
(b) xylem
(c) both (a) and (b)
(d) none of these
Answer:
(a) stomata

Question 4.
Which are the four types of animal tissues?
(a) Epithelial, squamous, muscular, connective
(b) Epithelial, cardiac
(c) Connective, nervous
(d) Cuboidal, columnar
Answer:
(c) Connective, nervous

JAC Class 9 Science Important Questions Chapter 6 Tissues

Question 5.
Which of the myelin sheath?
(a) Blood
(b) Cartilage
(c) Tendon
(d) Neuron
Answer:
(d) Neuron

Question 6.
A group of cells alike in form, function and origin are called
(a) tissue
(b) organ
(c) organelle
(d) none of these
Answer:
(a) tissue

Question 7.
Which of the following tissues is composed of mainly dead cells?
(a) Phloem
(b) Epidermis
(c) Xylem
(d) Endodermis
Answer:
(c) Xylem

Question 8.
Phloem in the plants performs the function of
(a) conduction of food
(b) conduction of water
(c) providing support
(d) photosynthesis
Answer:
(a) conduction of food

Question 9.
Which of the following tissues forms glands?
(a) Epithelial
(b) Connective
(c) Nervous
(d) Muscle
Answer:
(a) Epithelial

Question 10.
The end of a long bone is connected to another bone by
(a) ligament
(b) tendon
(c) cartilage
(d) nuclei
Answer:
(a) ligament

Question 11.
Which of the following cells are living cells?
(a) Fibres
(b) Vessels
(c) Collenchyma
(d) all of these
Answer:
(c) Collenchyma

Question 12.
How many guard cells enclose a stoma?
(a) One
(b) Two
(c) Three
(d) Four
Answer:
(b) Two

Question 13.
Which of the following cells helps sieve tubes to translocate food?
(a) Xylem parenchyma
(b) Phloem parenchyma
(c) Phloem fibre
(d) Companion cell
Answer:
(d) Companion cell

Question 14.
A neuron consists of
(a) cell body
(b) dendrites
(c) axon
(d) all of these
Answer:
(d) all of these

Question 15.
Nerve cell does not contain
(a) nerve endings
(b) tendons
(c) axon
(d) dendrites
Answer:
(b) tendons

Analysing & Evaluating Questions

Question 16.
While doing work and running, you move your organs like hands, legs et(c) Which among the following is correct?
(a) Smooth muscles contract and pull the ligament to move the bones.
(b) Smooth muscles contract and pull the tendons to move the bones.
(c) Skeletal muscles contract and pull the ligament to move the bones.
(d) Skeletal muscles contract and pull the tendon to move the bones.
Answer:
(d) Skeletal muscles contract and pull the tendon to move the bones.

JAC Class 9 Science Important Questions Chapter 6 Tissues

Question 17.
A nail is inserted in the trunk of a tree at a height of 1 metre from the ground level. After 3 years the nail will.
(a) move downwards.
(b) move upwards.
(c) remain at the same position.
(d) move sideways.
Answer:
(c) remain at the same position.

Question 18.
You are asked to observe the permanent slides of parenchyma and sclerenchyma tissues. You will identify the slide containing sclerenchyma tissue by locating.
(a) thickened cell walls
(b) size of the cells
(c) position of nucleus
(d) size of nucleus
Answer:
(a) thickened cell walls

Assertion Reason Questions

Directions: In the following questions, the Assertions and the Reasons have been put forward. Read the statements carefully and choose the correct alternative from the following:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.
(C) The assertion is true but the reason is false.
(D) Both the statements are false.
1. Assertion: Meristematic tissues are found in the growing tips of roots and shoots of a plant.
Reason: Meristematic tissues are composed of cells having the ability of cell division.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

2. Assertion: Outer protective layer of plants is made up of epidermal tissues.
Reason: Epidermal tissue is always composed of dead cells.
Answer:
(C) The assertion is true but the reason is false.

3. Assertion: Xylem shows unidirectional transport of materials.
Reason: Tracheids and vessels of xylem consist of dead cells.
Answer:
(B) The assertion and the reason are correct but the reason is not the correct explanation of the assertion.

4. Assertion: Ligament is a fibrous connective tissue.
Reason: Ligament connects muscle with skin.
Answer:
(C) The assertion is true but the reason is false.

5. Assertion: Peristalsis of food pipe is an involuntary action.
Reason: Food pipe is made up of smooth muscles.
Answer:
(A) Both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

Very Short Answer Type Questions

Question 1.
Name the three types of meristematic tissues.
Answer:
Apical, lateral and intercalary tissues.

Question 2.
Where is apical meristem found?
Answer:
It is present at the growing tips of stem and root it increases the length of the stem and roots.

Question 3.
Name the two types of plant tissues.
Answer:
Meristematic tissue and permanent tissue.

Question 4.
Define tracheids.
Answer:
A tracheid is a tubular cell in a vascular plant that carries water and minerals from the roots to the rest of the plant. lt also provides structural support.

JAC Class 9 Science Important Questions Chapter 6 Tissues

Question 5.
Write the names of various types of blood cells.
Answer:
There are three types of blood cells: RBCs, WBCs, and Platelets.

Question 6.
What are guard cells?
Answer:
Each stoma is bounded by a pair of specialised kidney-shaped epidermal cells called guard cells.

Question 7.
Write the main function of meristematic tissue.
Answer:
The main function of meristematic tissue is to form new cells continuously for increasing cell number, length and the girth of the plant.

Question 8.
Define simple permanent tissue.
Answer:
It consists of one type of cells which look like one another.

Question 9.
Give three types of simple permanent plant tissues.
Answer:
(a) Parenchyma
(b) Collenchyma
(c) Sclerenchyma

Question 10.
What are the main functions of vascular tissues in plants?
Answer:
Vascular tissues transport:

  1. Water and dissolved minerals from roots to various parts of the plant (xylem).
  2. Prepared food material from leaves to different plant parts (Phloem).

Question 11.
Define vascular bundles.
Answer:
In plants, complex tissues xylem and phloem, together constitute a structure called vascular bundle. Their main function is transportation of water, minerals and food materials within plant body.

Question 12.
Define xylem.
Answer:
Xylem is a complex plant tissue which transports water and dissolved minerals from roots to all other plant parts.

Question 13.
What are muscular tissues?
Answer:
These are specialised tissues which are composed of contractile, fibre – like cells. These tissues are responsible for movement in our body.

Question 14.
What are the main functions of muscular tissue?
Answer:
The main function of muscular tissue is the movement of the body or limbs which is brought about by contraction and relaxation of contractile proteins present in muscle cells.

Question 15.
Which type of muscles is the stomach wall made up of?
Answer:
Smooth or non – striated muscles. They are involuntary muscles.

Question 16.
What are the two main features of connective tissue?
Answer:
Main features:

  1. Cells are loosely spaced and are embedded in matrix.
  2. Matrix may be jelly – like, fluid, dense or rigid.

Question 17.
Which cell may be longest in the body of an animal?
Answer:
Neuron (nerve cell) which may be up to 1m long (in special cases).

Analysing & Evaluating Questions

Question 18.
If the tip of sugarcane plant is removed from the field, even then it keeps on growing in length. Explain why?
Answer:
The sugaracane plant keeps growing due to the presence of intercalary meristem which is responsible for increase in intemodal length.

Question 19.
If a potted plant is covered with a glass jar, water vapours appear on the inner wall of glass jar. Explain why?
Answer:
Plants lose water through the aerial parts by the process known as transpiration. If the potted pant is covered with a glass jar, the water vapours cannot escape outside and stick to the cooler inner walls of glass jar due to condensation.

Question 20.
Water hyacinth floats on water surface. Explain.
Answer:
In aquatic plants like water hyacinth, a type of parenchyma tissue called aerenchyma is present. It develops air spaces in these plants to provide them buoyancy so that they can float easily on the surface of water.

Short Answer Type Questions

Question 1.
Differentiate between bone and cartilage.
Answer:

Bone Cartilage
(a) It is hard. (a) It is soft.
(b) Matrix has an inflexible material. (b) Matrix has a flexible material.
(c) Matrix always contains calcium salts. (c) Calcium salt may or may not be present in the matrix.
(d) Bones have rich blood supply. (d) Cartilages do not have rich blood supply.

Question 2.
What are the functions of areolar tissue?
Answer:
Functions of areolar tissue are as follows:

  1.  It fills the space inside the organs, thus acts as a packing tissue between the organs.
  2.  It supports many delicate organs in the body.
  3.  It plays role in repair of tissues.

Question 3.
Write differences between xylem and phloem.
Answer:

Xylem Phloem
(a) It contains mainly dead elements. (a) It consists of mainly living elements.
(b) It conducts water and minerals. (b) It conducts food.
(c) It provides mechanical strength to the plant. (c) It does not provide mechanical strength to the plant.

Question 4.
Why does epidermal tissue have no intercellular space?
Answer:
Epidermis is formed of single continuous layered cells. It covers without any intercellular space and protects all parts of the plant. Small pores called stomata are present on the leaf, and help in the exchange of gases and water. Epidermal cells on the aerial parts of the plant secrete waxy, water resistant layers on their outer surface. It checks the loss of water, mechanical injury and invasion by parasitic fungi. Roots commonly bear long hair like parts that increase the total absorptive surface area of water absorption.

Question 5.
Write the functions of different types of cells of xylem.
Answer:
Xylem consists of tracheids, vessels, xylem parenchyma and xylem fibres. Tracheids and vessels allow the transport of water and minerals. Xylem parenchyma stores food and helps in the sideways conduction of water. Xylem fibres are supportive in function.

Question 6.
State the difference between bone and blood.
Answer:

Bone Blood
(a) It is a hard tissue. (a) It is a liquid tissue.
(b) It consists of osteocytes. (b) It consists of plasma, RBC, WBC and blood platelets.
(c) It helps in movement and support of the body. (c) It helps in the transport of substances.

Question 7.
What are the characteristic features of meristematic cells?
Answer:
Meristematic cells have:

  1. Thin cell walls.
  2. Abundant or dense cytoplasm and single large nucleus.
  3. Spherical, oval, polygonal or rectangular shape.
  4. No intercellular spaces between them.
  5. Either no vacuole at all or a few vacuoles.

Question 8.
How many types of meristems are present in plants, on the basis of position? Show diagrammatically.
Answer:
On the basis of location of meristem, it is classified into three types:

  1. Apical meristem: It is present at the tip of stem, root and their branches.
  2. Intercalary meristem: It is found at the leaf base, above the nodes (i.e, at the base of intemodes like in grasses) or below the nodes (i.e., at the uppermost region of intemodes like in mint). Apical meristem
    JAC Class 9th Science Solutions Chapter 6 Tissues h
  3. Lateral meristem: Vascular cambium and cork cambium are examples of lateral meristem. Vascular cambium is found in vascular bundles, while cork cambium is found underneath the bark of trees. Both of these cause increase in girth of plants.

Question 9.
What are permanent tissues?
Answer:
The cells of meristematic tissue lose the ability to divide and get differentiated into specialised cells. These differentiated cells form different types of tissues which are known as permanent tissues. Some examples of permanent tissues are parenchyma, sclerenchyma, etc.

JAC Class 9 Science Important Questions Chapter 6 Tissues

Question 10.
Give the main functions of parenchyma The main functions of parenchyma are as follows:
Answer:

  1. Chlorenchyma contains chloroplast which helps in photosynthesis.
  2. Parenchyma cell stores food in the form of starch, proteins, oils and fats.
  3. It helps in floating of aquatic plants due to presence of aerenchyma tissue.
  4. Idioplasmic cell secretes resins, latex, tannin, oils, etc.
  5. Parenchyma of xylem and phloem helps in transport of nutrition and water.
  6. Parenchyma tissue provides mechanical support.

Question 11.
Define the structure of sclerenchyma Write its major functions.
Answer:
Sclerenchyma (scleras – hard) is the chief mechanical tissue of plants. It is a permanent tissue. The cells are made up of sclerenchymatous tissue. The cells are usually long, narrow, pointed at both ends and uniformly thickened by the deposition of lignin without any space in between the cells. The walls are often very highly thickened so that the lumen or cell cavity is nearly obliterated. They are usually provided with simple pits which may be oblique or straight.
JAC Class 9th Science Solutions Chapter 6 Tissues i

  1. Sclerenchyma is made up of dead and lignified cells which provide support to plants.
  2. It provides hardness to stony fruits such as nuts, coconut, almonds, etc.

Question 12.
What are the main functions of collenchyma?
Answer:
The main function of collenchyma is to provide mechanical support, tensile strength, elasticity and flexibility to stem, leaf stalks and leaves.

Question 13.
What are the four main functions of epithelial tissues?
Answer:
Epithelial tissue covers the body surface and forms the lining for most internal cavities. The major function of epithelial tissue includes protection, secretion, absorption and filtration. The skin is an organ made up of epithelial tissue which protects the body from dirt, dust, bacteria and other microbes that may be harmful.

Question 14.
Differentiate between voluntary and involuntary muscles.
Answer:
Voluntary muscles are those which are directly under control of our conscious will, e.g., skeletal muscle. They work or move on our command. Involuntary muscles are not directly under command of our will. We cannot stop contraction or restart contraction of the stomach, intestine or heart muscles. They are of two types cardiac and smooth muscles. Smooth muscles are found in stomach, intestine, and iris of eyes, in ureter and in the bronchi of lungs. Another type of involuntary muscles, i.e, cardiac muscles are found in heart.

Question 15.
Name three types of muscle tissues and give functions of each.
Answer:
The three types of muscle tissues are:

  1. Striated muscles: These muscles show alternate light and dark bands or striations. They are voluntary muscles and present in skeletal tissues, help in movement of body and bones.
  2. Smooth muscles: These are involuntary muscles; control the movement of food in alimentary canal, contraction and relaxation of blood vessels are present in iris, uterus, etc.
  3. Cardiac muscles: These muscles are present in heart, help in the rhythmic contraction and relaxation of heart throughout the life.

Question 16.
What are the two main components of blood? Why is blood considered a type of connective tissue?
Answer:
Blood has two main components:

  1. Fluid (liquid) matrix called plasma.
  2. Suspended red blood cells (RBCs), white blood cells (WBCs) and platelets.
    • Blood is considered as a connective tissue because it has the same origin as the other connective tissues have.
    • It flows to different parts of the body and thus connects different parts of the body with one another to exchange materials and gases.

Analysing & Evaluating Questions

Question 17.
Animals of colder regions and fishes of cold water have thicker layer of subcutaneous fat. Describe why?
Answer:
The animals of colder regions are subject to more heat loss due to very low temperature. The subcutaneous fat under the dermis layer of the skin forms an insulating layer against the extremely cold environment and also acts as a food store.

Question 18.
Due to excessive workout, an athlete was suffering from fatigue. He was suggested to take rest for some time and then again join the practice.
(a) Why did the athlete feel tired after excessive workout?
(b) Why was he asked to take rest and then join the practice again?
Answer:
(a) The skeletal muscles of our limbs are responsible for body movement. These muscles have power and contract very fast. The excessive activity and lack of oxygen supply to the muscles makes them tired soon. This results in the accumulation of lactic acid in the muscles which keeps them in the state of inactivity and tiredness.

(b) While he is on rest, the body regains the oxygen supply to the muscle cells. The lactic acid deposited in the muscles is then transported by blood to the liver, where it is converted to glycogen (a carbohydrate).

Long Answer Type Questions

Question 1.
Give the flow chart of plant tissues.
Answer:
JAC Class 9th Science Solutions Chapter 6 Tissues j

Question 2.
What is connective tissue? Explain its types.
Answer:
A connective tissue consists of different types of cells. The different types of connective tissues are as follows:
JAC Class 9th Science Solutions Chapter 6 Tissues k
1. Blood: It has a fluid matrix called plasma in which RBCs, WBCs and platelets are suspended, Blood transports gases, digested food, hormones and waste materials to different body parts.

2. Bone: This connective tissue forms the framework that supports the body. It also anchors the muscles and supports the main organs of the body

3. Ligament: This connective tissue connects the two bones. This is very elastic having considerable strength.

4. Tendon: It connects muscles to bones. It is a fibrous tissue with great strength but limited flexibility.

5. Cartilage: It has widely spaced cells. It smoothens bone surfaces at joints and is also present in the nose, ear, trachea and larynx.

6. Areolar tissue: It is a connective tissue which consists of matrix, several types of cells, collagen and elastin fibres. It is found between the skin and muscles, around blood vessels and nerves and in the bone marrow. It fills space inside the organs, supports internal organs and helps in repair of the tissues.

7. Adipose tissue: It consists of cells (adipocytes) which are filled with fat globules. These cells remain scattered in a matrix. It is found below the skin and between internal organs. It stores fats and acts as an insulator.
JAC Class 9th Science Solutions Chapter 6 Tissues l

Question 3.
Show the types of animal tissues through flow chart.
JAC Class 9th Science Solutions Chapter 6 Tissues m

Question 3.
Why is epidermis considered a protective tissue?
Epidermis is considered a protective tissue because its prime purpose is to form a physical barrier between the outside and inside of the body. These tissues are usually present in the outermost layer of the plant body such as leaves, stem and roots. It is one cell thick and covered with cutin and protects the underlying tissues present in the plant body. As roots and stems grow older with time, tissues at the periphery become cork cells. Cork cells are dead, have no intercellular spaces and the cell walls are heavily thickened by the deposition of suberin. They prevent loss of water.

JAC Class 9 Science Important Questions Chapter 6 Tissues

Question 5.
Describe the complex tissue of plants.
Answer:
Complex permanent tissue is composed of two or more than two types of cells and contributes to a common function. It is also known as vascular tissue Xylem and phloem are the two complex tissues.

  1. ylem: Xylem is composed of four types of cells tracheids, vessels, xylem fibres and xylem parenchyma Most of these cells are dead. Tracheids and vessels help in water transportation, parenchyma cells are mainly supportive in function.
  2. Phloem: Phloem is made up of four types of elements sieve tubes, companion cells, phloem fibres and phloem parenchyma It helps in the transportation of food in both the directions, i.e., from leaves to roots and to other parts of the plant.

Question 6.
Observe the diagrams and answer the questions given below.
JAC Class 9th Science Solutions Chapter 6 Tissues n
(a) What kind of cells are there in shoot apex and root apex?
(b) What are the main characteristics of these cells?
Answer:
(a) Meristematic cells.

(b) Cells have big nucleus and dense cytoplasm. These cells lack intercellular spaces and vacuoles.

Question 7.
Describe the characteristics of parenchyma What are its major modifications?
Answer:
Characteristics of parenchyma tissue:

  1. Living tissue.
  2. Shape spherical, oval, rectangular, polygonal, elongated or irregular in shape.
  3. Cell wall a thin wall made up of cellulose, hemicellulose and pectin.
  4. Young parenchymatous cells are loosely arranged.
  5. Intercellular space is present.
  6. Cells store reserve food material.
  7. Parenchyma is found in all parts of plant such as cortex, pith, palisade, mesophyll, flower, seed, etc.
  8. It is also found in vascular tissues.

Two modifications of parenchyma are chlorenchyma and aerenchyma.

  • Chlorenchyma: Sometimes cells of the parenchyma contain chlorophyll and perform photosynthesis. This kind of parenchyma is known as chlorenchyma.
  • Aerenchyma: In aquatic plants, parenchyma contains big air spaces in between them. Such a parenchyma tissue is known as aerenchyma

Analysing & Evaluating Questions

Question 8.
Bharti was asked to identify the following blood cells as erythrocytes, thrombocytes and types of leucocytes.
(a) On what basis was she able to identify erythrocytes?
(b) Which cells are shown by the labels B, C and D?
(c) What are the functions of E and F?
(d) Write any characteristic feature of G.
JAC Class 9th Science Solutions Chapter 6 Tissues 14
Answer:
(a) Erythrocytes or red blood cells are biconcave, disc – shaped and without nucleus.

(b) B, C and D represent neutrophils, eosinophils and basophils, respectively. These are types of leucocytes called granulocytes.

(c) E – Monocytes engulf bacteria and cellular debris at the injured site on the body. F – Lymphocytes produce antibodies and provide immunity.

(d) G – Blood platelets are colourless, non – nucleated, small or round – shaped cells. They play role in blood coagulation.

Activity 1

  • Take two glass jars and fill them with water.
  • Now, take two onion bulbs and place one on each jar, as shown in the given figure.
  • Observe the growth of roots in both the bulbs for a few days.
  • Measure the length of roots on day 1, 2 and 3.

JAC Class 9th Science Solutions Chapter 6 Tissues 15
On day 4, cut the root tips of the onion bulb in jar 2 by about 1 cm. After this, observe the growth of roots in both the jars and measure their lengths each day for five more days and record the observations in table, as shown below. Growth of roots in onion bulb:

Length Day 1 Day 2 Day 3 Day 4 Day 5
Jar 1
Jar 2

 

Observations

  • Onion in Jar 1 has longer roots because they keep on growing due to the presence of root tips.
  • Roots stop growing in onion in Jar 2 as their root tips are removed.
  • The tips stop growing in Jar 2 after we cut them because the apical meristem which causes increase in length of roots is removed.

Activity  2

  • Take a plant stem and with the help of your teacher, cut very thin slices or sections of it.
  • Now, stain the slices with safranin. Place one neatly cut section on a slide, and put a drop of glycerine.
  • Cover with a cover – slip and observe under the microscope. Observe the various types of cells and their arrangement and compare them.

Observations

  • All cells are not similar in structure; we see a variety of cells with different shapes and sizes.
  • We can see at least 8 – 10 different types of cells in the slide.
  • There are varieties of cells so that each group of cells does a specific role in the overall growth of plant.

JAC Class 9th Science Solutions Chapter 6 Tissues 16

Activity 3

  • Take a freshly plucked leaf of Rhoeo.
  • Stretch and break it by applying pressure.
  • While breaking it, keep it stretched gently so that some peel or skin projects out from the cut.
  • Remove this peel and put it in a petri dish filled with water.
  • Add a few drops of safranin.
  • Wait for a couple of minutes and then transfer it onto a slide. Gently place a cover slip over it.
  • Observe under microscope.

JAC Class 9th Science Solutions Chapter 6 Tissues 17
Observations
The epidermis is the outermost covering, usually made of a single layer of cells. The epidermis of leaf bears small pores called stomata.

Value Based Questions

Question 1.
A group of students completed the project of finding the botanical name of all the trees present in the school campus. They prepared metal plates with name carved on it, to fix it on the plant trunks. Shreya was concerned that if the metal plate is fixed into tree many cells of the tree may get damaged. But the group members explained her that the outer layer of trunk does not have living cells and there won’t be any damage to the tree.
1. What types of cells are present on the outer layer of the bark/tree trunk?
2. How does the cork act as a protective tissue?
3. What value of the group is seen in the above case?
Answer:

  1. On the outer layer of tree/trunk a thick layer of dead cells is present which acts as a protective tissue.
  2. In cork, all cells are dead without intercellular spaces and the walls of the cells have deposition of suberin.
  3. The students in a group show team effort, learning and co – operation.

Question 2.
A paralytic patient was unable to walk. The family members of the patient took the utmost care of the patient.
(a) Name two tissues responsible for the movement of a body.
(b) Name the tissues present in brain and spine.
(c) What value of the family members is seen in the above case?
Answer:
(a) The two tissues responsible for movement of the body are muscular tissue and nervous tissue.
(b) The tissues present in brain and spines are nervous tissues.
(c) The family member showed the value of caring, responsibility, dutiful and kindness.

JAC Class 9 Science Important Questions