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A man rowing a boat upstream is at rest with respect to the shore. (a) Is he doing any work? (b) If he stops rowing and moves down with the stream, is any work being done on him?

A man rowing a boat upstream is at rest with respect to the shore. (a) Is he doing any work? (b) If he stops rowing and moves down with the stream, is any work being done on him?

Grade:11

3 Answers

Aditi Chauhan
askIITians Faculty 396 Points
8 years ago
Yes he is doing some work. To rowing a boat upstream, the man applies some force against the stream. The direction of the stream is downward while the direction of boat is upward. So there is relative motion between the downstream and boat even though the man is at rest. Therefore the man is doing some work.
No, there is no work being done him. The man stops rowing results the displacement of the boat in upstream direction is zero. Again since the boat moves down with the stream, so a force will act in the direction of downstream results a negative work will act on the boat by flowing water. Therefore the sum of both works on the boat will be zero. Thus there is no work being done him.
Hajra
15 Points
5 years ago
I think he is doing work because he is moving against the force of stream ..since he is at rest with respect to shore but not with respect to the moving stream.
Dilbar Khan
15 Points
5 years ago
No work is done by the man rowinga Boat upstream when he is at rest with respect to the sure because work is the scalar product of force and displacement so we know that work done is 
W=Fdcos0
So the force applied by the on the boat produces no displacement but balance the force of water so the word done is.
W=F×0×cos0
W=0
Hence no work is done by the man keeping the boat at rest with respect to the Shore
 

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