A boy of mass 50 kg runs up a staircase of 45 steps in 9 s. If the height of each step is 15 cm, find his power. Take g = 10 m s–2 .

Solution:
Weight of the boy,
w = mg = 50 kg × 10 m s^–2 = 500 N
Height of the staircase,
h = 45 × 15/100 m = 6.75 m
Time taken to climb, t = 9 s, power, P = Work done/time taken mgh / t

Power (P) = (500 N × 6.75 m ) / 9s
= 375 W.
Power is 375 W