In which of the following activities is zero work said to be done?

Man pushing the vertical wall
Sleeping for numerous hours
While walking a man holding an object.
All of the above

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a, b

a, c

b, d

answer is D.

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Detailed Solution

The zero work is said to be done only in all cases.
In the case of

a

, if you push a wall and it doesn't move, you haven't accomplished anything. Man pushing the vertical wall. (The force applied by the man will be perpendicular).
In the case of

b

, Sleeping for numerous hours is another example of not working because there is no change in displacement as well as there is no change in kinetic energy while you are sleeping. (The gravitational force will be perpendicular).
In the case of

c

, While walking, a man is holding an object. The displacement of a person running forward on a horizontal surface. (The gravitational force will be perpendicular).

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