# Homework Help: Potential energy

1. Jul 14, 2004

### AcEY

This maybe an easy question for you, but for me im having trouble. Im working on 2D projectile motion and i need an equation to work out the inital velocity when i have the PE.

2. Jul 14, 2004

### maverick280857

Where are you stuck?

The potential energy at a verticle height y above the datum is equal to mgy. The kinetic energy is (1/2)*m*v^2. If you want, you can use the following expression for y

$$y = y_{0} + (V_{0}\sin \theta)t - \frac{1}{2}gt^{2}$$

and substitute it into U = mgy and solve for $$V_{0}$$, the initial velocity.