Question

2. A man who has a mass of 80 kg can run up a flight of stairs of 20 steps in 5 seconds. Given the each steps in 20cm high, how much power does the man use to run up the flights of stairs?

Answer 1

By definition, the power is:

$$P = \dfrac{W}{t}$$

where $W$ is the work done by the man, and $t = 5s$ is the time. In order to run up the stairs the man should do the following work:

$$W = mgh$$

where $m = 80kg$ is the mass of the man, $g = 9.8m/s^2$ is the gravitational acceleration, and $h = 20\cdot 20cm = 4m$ is the total height of the stairs. Thus, obtain;

$$P = \dfrac{mgh}{t} = \dfrac{80\cdot 9.8\cdot 4m}{5s} \approx 627W$$

Answer. 627W