A 70 kg man runs up a long flight of stairs in 4 s. vertical height of the stair is 4.5 m. Calculate his power. (P = 7.7 ｘ 10² Watts) 


Given:

Mass of the man = m = 70 kg
Time = t = 4 s
Height of stair = h = 4.5 m 
Value of g = 9.81 ms⁻²

To Find:

Power of man = P = ?



Solution:

Power is defined as the rate with respect to the time at which work is done. The mathematical formula of power is given by:

P = `\ frac{Work}{Time}`

P = `\ frac{W}{t}`  ------------(1)

but here all the work is done due to gain in potential energy so,

W = Gain in P.E. = mgh, therefore equation (1) will be

P = `\ frac{mgh}{t}` 

by putting values

P = `\ frac{70 kg ｘ 9.81 ms⁻²ï½˜ 4.5 m}{4 s}` 

P = 772. 537 kg m² s⁻³            [kg m² s⁻³ = W (watt)]

or

P = 7.7 ｘ 10² W ------------------Ans




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