A labourer climbs up a staircase carrying a load of 10 kg on his head. The staircase has 20 steps and each step is 0.2 m high. Find the work done by the labourer in carrying the load. (g = 10 m s^–2)

Load is lifted against gravity, hence, work is done against the gravitational force.

∴ Work done = mgh = potential energy

Height of one step = 0.2 m

Height of 20 steps = Total height = h = 20 × 0.2 = 4 m

m = 10 kg

∴ Work done = mgh = 10 × 10 × 4 = 400 J