Question

A boy of mass m climbs up the stairs of vertical height h.

(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?

Answer 1

(a) W=mgh

The force of gravity on the boy is F = mg acting vertically downwards and the displacement in the direction opposite to force (i.e., vertical) is S = −h. Therefore the work done by the force of gravity on the boy is W = FS = −mgh or, the work W = mgh is done by the boy against the force of gravity.

(b) The work done would have been the same as the work done by gravity doesn't depend on the path. It only depends on initial and final positions.