(a) What is the work done by the boy against the force of gravity?

(b) What would have been the work done if he uses a lift in climbing the same vertical height?

Solutions:

Allow a boy with mass m to ascend a vertical height h using either a stairway or a lift. The force of gravity acting vertically downwards is F = mg, while the vertical displacement in the opposite direction is

We have, S = – h

Hence, the work done by the force of gravity on a boy is given by –

W = FS = – mgh

The work mgh is done by a boy against the force of gravity.