A 50 kg man moved 25 steps up in 20 seconds. Find his power, if each step is 16 cm high. Ans. (100 W)


Given:  

Mass of the man= m =  50 kg
No. of steps he move = n = 25 
Height of one step =  0.16 m
Total height of steps that the man moves = h = 25 x 0.16 m = 4 m
Time taken  = = 20 sec
gravitational acceleration = g = 10 m s²

To Find:

Power of the man = P = ?  Watt

Solution:   

As Power is defined as the rate of doing work. So,

P = `\frac {W}{t}`

P = `\frac {F xS}{t}`   (∴ Force = F = weight = W = mg and S = h)

P = `\frac {mgh}{t}`

by putting values 

P = `\frac {50 kg x 10 m s⁻² x4 m}{20 s}`

P =  100 kg m² s⁻³  

or

P = 100 W 

Thus the power of the man is 100 W

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