A boy of mass 50 kg runs up a staircase of 45 steps in 9 s. If the height of each step of the staircase is 15 cm, find the power of the boy.
Given, mass of body, m = 50 kg
h = 45 x15 = 675 cm = 6.75 m
t = 9 s, g = 10 m
PE = mgh = 50 x 10 x 6.75 = 3375 J
Power of the body = PE / time = Energy / time = 3375 / 9 = 375 W
why is potential energy substituted for energy spent when the body is in motion