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Question

A man has power of 90W and mass 60kg runs up a staircase in 40 second. If each step of staircase is 20m high calculate the number of steps

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Solution

Given power =90 W, mass = 60 kg, time taken = 40 second, each step height =20 cm, let x = number of stairs in staircase. g = acceleration due to gravity = 10 m/s2 (approx)
power = work done / time
work done = p ×t = 90 ×40 = 3600 J
work done = F× s = mg × s = 60×10×(x × 20)
3600 = 600 ×0.2 × x
x = 3600 /(600 ×0.2) =
we get
x = 20

no. of stairs are 20.

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