A man is rowing upstream and is at rest w.r.t. shore. Is he doing work w.r.t. shore?
The man is doing zero work because he is at rest w.r.t. shore. Hence, displacement is zero.
Therefore work done by the man is zero.
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By eating two apples, a person starts pushing the wall of room. If food value of apple is 100 calories per apple, how much work he will do in pushing the wall in one hour?
Zero, because the displacement of the wall will be zero.
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Is frictional force conservative?
Friction is a non-conservation force because work done by friction over closed path is not equal to zero.