Q38 of 805 Page 156

A motor car, with its glass totally closed, is parked directly under the sun. The inside temperature of the car rises very high. Explain why?

OR


What are the causes of water pollution? Discuss how can you contribute in reducing the water pollution.

Rise in temperature inside the car happens due to the greenhouse effect. Infrared radiations of the sunlight, having smaller wavelength, pass through the glass and heat the inside of the car. The radiation reflected by the inside of the car having longer wavelength, cannot pass out of the glass. Hence the heat gets trapped inside and raises the temperature.


OR


The causes of water pollution-


a) Water dissolves the fertilizers and pesticides that are used in farms. So, some percentage of these substances are washed into the water bodies causing pollution of water.


b) Sewage from the towns, cities, wastes from factories are also dumped into rivers and lakes.


c) Specific industries also use water for cooling in various operations and later return this hot water to water to water bodies.


d) The temperature difference in water affects the life forms that are found in water bodies in various ways. This affects the balance between various organisms which had been established there.


Measures to reduce water pollution-


a) Sewer lines should not be directly connected to water bodies.


b) Garbage or domestic wastes should not be thrown in water bodies.


c) Plantation of trees near the banks of the river should be promoted to check soil erosion.


d) Dumping of toxic substances in the water bodies by industrial units must be checked.


More from this chapter

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36

(a) Explain the meaning of inertia with the help of an example.

(b) Two balls of 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? Give reasons for your answer.


OR


(a) A ball of mass m is thrown vertically upward from the ground with an initial speed v, its speed decreases continuously till it becomes zero. Thereafter, the ball begins to fall downward and attains the speed v again before striking the ground. It implies that the magnitude of initial and final momentum of the ball are same. Yet, it is not an example of conservation of momentum. Explain why?


(b) A bullet of mass 20 g is horizontally fired with a velocity 150 m s–1 from a pistol of mass 2 kg. What is the recoil velocity of the pistol?

 37

(a) With the help of Second Law of Motion and the Universal Law of Gravitation derive an expression for acceleration due to gravity ‘g’.

(b) The weight of any person on the moon is about 1/6 times that on the earth. He can lift a mass of 15 kg on the earth. What will be the maximum, mass, which can be lifted by the same force applied by the person on the moon?


OR


(a) Identical packets are dropped from two aeroplanes, one above the equator and the other above the north pole, both at height ‘h’. Assuming all conditions are identical, will these packets take same time to reach the surface of the earth? Justify your answer.


(b) It is seen that a falling apple is attracted towards the earth. Does the apple also attract the earth? If so, we do not see the earth moving towards the apple. Why?

 1

Seema visited a Natural Gas Compressing Unit and found that the gas can be liquefied under specific conditions of temperature and pressure. While sharing her experience with friends she got confused. Help her to identity the correct set of conditions.

 2

Which of the following are physical changes?

(i) Melting of iron metal


(ii) Rusting of iron


(iii) Bending of an iron rod


(iv) Drawing a wire of iron metal