From the activities listed below, in which of the following cases is the work said to be done?

An apple is falling off a tree.
A girl is pushing a book on a table.
A horse is pulling a cart.
Sunil is reading a book.
A man is pushing a wall.
A man is holding a bucket of water.
A porter is carrying a load on his head.
A coolie is carrying a load on his head.
A man is climbing the stairs.
A ball is thrown upwards in the air.

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a, b, c, h, i, j

b, h, i, j, e

c, h, i, j, d, a

b, c, h, i, a, j

answer is D.

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Detailed Solution

The correct option is

1

.
From the above options provided, work is done in options a,b, c, h, i, j.
In option a, The potential energy is present in an apple hanging from a tree because of its elevated position. When an apple is dropped from a tree, it has kinetic energy. As a result, when the apple falls, the potential energy previously stored in its raised position is converted into kinetic energy. When the apple strikes the stone, this kinetic energy causes the stone to move into the ground.
In option b, moving the book up with force exerted by your hand would work on the book. The reason you wouldn't do any work when you push the book down is that it is not moving. More precisely, it is not moving in the same direction as the force you applied.
In option c, work is done by the bullock as the direction of force is applied, and the direction of the displacement of the cart is in the same direction. The product of force and displacement will give the work done by the bullock.
In option d, no work is done by Sunil because no force is exerted on the book.
In option e, no work is done by the man because the wall doesn't cover any distance on exertion of the force.
In option f, no work is done because the man doesn't cover the distance.
In option g, no work is done by the porter because the porter is carrying the load perpendicularly and

\cos 90 ° = 0

.
In option h, work is done by the kite because a force is exerted on the kite, and it also covers some distance.
In option i, work is done by the man climbing the stairs as the force exerted by him on the ground helps the man climb the stairs.
In option j, work is done as the gravitational force acts on the ball and covers some distance.

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