Question

In which of the following cases no work is done by the force?

• A. A man carrying a bucket of water, walking on a level road with a uniform velocity.
• B. A drop of rain falling vertically with a constant velocity.
• C. A man whirling a stone tied to a string in a circle with a constant speed.
• D. A man walking upon a staircase

Answer 1

Answer: (A), (B), (C)

The correct options are
A A man whirling a stone tied to a string in a circle with a constant speed.
B A man carrying a bucket of water, walking on a level road with a uniform velocity.
C A drop of rain falling vertically with a constant velocity.

In first three cases displacement is perpendicular to the direction of force and as,

$W=FS\cos 0$

$W=0$

but when man moves upon the stair be pushes himself forward and upward too. So a displacement in the direction of force generates, So some amount of work is done here.