Question

A pupil of mass 50kg runs a flight of 20 stairs each 25cm high in a time of 20 seconds,[Take g=10/kg ] calculate the pupil's gain in potential energy and the useful power developed by the pupil in climbing the stairs.

Answer 1

20 * 0.25 = 20/4 = 5 meters up
gain in PE = m g h = 50 * 10 * 5 = 2500 Joules
power = energy/time = 2500 Joules / 20 seconds = 250/2 = 125 watts