Question

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

Answer 1

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 = $10m/s^2$ (approx.)
Power = $\frac{workdone}{time}$
Work done = $p\times t=90\times 40=3600J$
Work done = $F\times s=mg\times s=60\times 10\times (x\times 0.2)$
$3600=600\times 0.2\times x$
$x=\frac{3600}{(600\times 0.2)}=30$
Number of steps is 30.