# Power Help

1. Oct 16, 2007

### engineer2010

1. The problem statement, all variables and given/known data
Water falls onto a water wheell from a height of 2.0m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is the max power output. (b) What is the speed as it hits the wheel?

2. Relevant equations

Ep= mgh Ek= 1/2mv^2

3. The attempt at a solution

I know that the water initally has both potential and kinetic energy as it falls but i am unsure as to how i use the rate in these equations and also which power equation(s) I use once i get to that stage.

2. Oct 16, 2007

### Staff: Mentor

Well the elevation of a mass m in a gravitational field provides for gravitational potential energy (GPE) by virtue of mgh, where h is the elevation above some reference point.

If an object at h is released and it falls through distance h, then GPE decreases by mgh and that GPE is transformed to kinetic energy 1/2 mv2, and neglecting air resistance mgh = 1/2 mv2.

If one has a mass flow rate $\dot{m}$, then the rate at which energy (described above) is delivered is simply $\dot{m}$gh, and the rate of energy delivery/transformation is power.