physics question

Question

It takes a 70kg man, 5 minutes to walk up 10 flights of stairs. If each flight of stairs has a height of 15m, what is the mans average power for this task?

Answer 1

Answer 2

Hello Sammie, I should be able to help you out. So this question directly asks you to calculate power. The power equation you should use here is P = W/t where W is the work done and t is the time elapsed while that work is being done. It takes the man 5 minutes to ascend those flights of stairs so t = 300 s.

Work is the change in energy of the system, or in this case, the man's change in energy. His velocity is never considered so we can ignore kinetic energy, but his potential energy does change. Starting at the ground his potential energy is 0 J but once he reaches the top his potential energy is PE = m*g*h where m is his mass, g is gravitational acceleration, and h is his height above ground (even though he is standing on a solid structure). The 10 flights of stairs which are each 15 meters means a total of 150 m above ground.

From there just calculate the potential energy change (final - initial) and divide by time and you will have Power in Watts (W). [note: Watts is Joules per second]