Q6 of 28 Page 159

When you lift a box from the floor and put it on an almirah the potential energy of the box increases but there is no change in its kinetic energy. Is it violation of conservation of energy? Explain.

No, there is no violation of conservation of energy. When force is applied to lift the box ,it is moving along the direction of action of force so, the acting force increases its energy as potential energy. When box falls down it loses its potential energy into kinetic energy.


More from this chapter

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4

What is mechanical energy?

 5

State the principle of conservation of energy.

 7

One person says that potential energy of a particular book kept in an almirah is 20 J and other says it is 30J . Is one of them necessarily wrong? Give reasons.

 8

In which of the following cases is the work done positive or zero or negative?

a) Work done by the porter on a suitcase in lifting it from the platform on to his head.


b) Work done by the force of gravity on suitcase as the suitcase falls from porter’s head.


c) Work done by the porter standing on platform with suitcase on his head.


d) Work done by force of gravity on a ball thrown up vertically up into the sky.


e) Work done by force applied by hands of a man swimming in a pond.