# Potential difference required to stop a particle

1. Mar 14, 2010

### Revvi

1. The problem statement, all variables and given/known data

A particle with a charge-to-mass ratio of 50 C/kg is moving at a speed of 200 m/s. What electric potential difference is required to stop the particle?

2. Relevant equations

F = Eq?

3. The attempt at a solution

I am completely uncertain how to start this problem. Perhaps somebody can start me off?

2. Mar 14, 2010

### xcvxcvvc

Remember that voltage is work per unit charge. Do you remember how to calculate the energy of a moving particle from your mechanics?

$$\frac{1}{2}mv^2=qV$$
To find q, you need to multiply mass into that charge per mass value. The unknown mass cancels on both sides.