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

Answer 1

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 $\times$t = 90 $\times$40 = 3600 J
work done = F$\times$ s = mg $\times$ s = 60$\times$10$\times$(x $\times$ 20)
3600 = 600 $\times$0.2 × x
x = 3600 /(600 $\times$0.2) =
we get
x = 20

no. of stairs are 20.