# Pendulum Problem with unknown angle

1. Oct 19, 2011

### jg727

A pendulum (with string length "L") and aball of mass "m" is pulled back to a horizontal position and then released. Assuming that θ is the angle between the string and the vertical, find the speed of the ball (v) at an angle of θ as a function of m,g,L, and/or θ.

I just can't get my mind around this problem.....

2. Oct 19, 2011

### Delphi51

Welcome to PF, jg!
I could be horrendous using motion formulas.
Have you considered an energy approach? The initial Ek is easy. Can you find the height when at angle θ and thus the potential energy? From that you can get the Ek at θ and then the speed.

3. Oct 19, 2011

### jg727

Thank You!
Ok, so I guess im actually having problems with finding the potential energy. I'm completely blanking.

4. Oct 19, 2011

PE = mgh