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

Options

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

Answer

A, B, C

Explanation

In options (a) and (c), no work is done because the force of gravity in option a. and the centripetal force in option c. are perpendicular to the direction of displacement. In option (b), no net force acts on the raindrop since it is falling with a uniform velocity, hence no work is done. In (d), the mass has to do work against gravity. Hence, the correct answers are (a), (b) and (c).