Q. A boy, of mass 50 kg, runs up a staircase of 45 steps in 10 s. If the height of each step is 14 cm, find his power. Take g= 10ms-2 ?

Explanation by: Tina Singh

Given, the mass of the body, m = 50 kg. h is the height, t is the time. g is the acceleration due to gravity which is aproximated to 10 m/s2 ? 
h = 45 × 14 = 630 cm = 6.30 m 
 t = 10 s, g = 10 ms-2 
 Potential Energy = mgh = 50 × 10 × 6.30 = 3150 J.
 (where J is the unit of energy/work which is joules)
 Power = PE / time = Energy / time = 3150 / 10 = 315 watt.
 (watt is the unit of power which is different from units)