# Power, mass, speed, time and height

1. Aug 29, 2011

### furor celtica

1. The problem statement, all variables and given/known data
A child of mass 30 kg runs up a flight of stairs in 6 seconds. The top of the flight is 3 metres above the bottom, and at the top he is running at 2ms^-1. What average power does he need to produce?

3. The attempt at a solution

This is one of the first exercises I have had to tackle concerning power, so I'm pretty sure its meant to be simple. However, in terms of power both force x velocity and work/time i have no idea where to start.

Without the child's starting speed, horizontal distance covered or total distance run I'm at a loss for what to use and what to look for...any suggestions would help.

2. Relevant equations

2. Aug 29, 2011

### PhanthomJay

The problem is vague about the child's initial speed. I assume since it gives the velocity at the top of the stairs and it talks about average power, that the child starts from rest and accelerates uniformly to reach her given speed at the top.

Buy you don't need horizontal or total distance to find work....you just need the vertical displacement....think about the work- energy equations.