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

From P=W/T ,W=FD,F=ma=50*10=500N,D=45*15=675cm/100=6.75m

W=FD=500*6.75=3375j

P=W/T=3375/9=375W![15171353869411723471457|281x500]