A boy of mass 50 kg runs up a staircase of 45 steps in 9 s

CBSE Class 9 CBSE Class 9 Science
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1

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.

2

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

3

why is potential energy substituted for energy spent when the body is in motion

4

From P=W/T ,W=FD,F=ma=5010=500N,D=4515=675cm/100=6.75m
W=FD=500*6.75=3375j
P=W/T=3375/9=375W![15171353869411723471457|281x500]