# Homework Help: Find q for a moving particle

1. Jan 29, 2013

### Rae_4

1. The problem statement, all variables and given/known data
A moving particle encounters an external electric field that decreases its kinetic energy from 8560 eV to 6770 eV as the particle moves from position A to position B. The electric potential at A is -50.5 V, and the electric potential at B is +25.9 V. Determine the charge of the particle. Include the algebraic sign (+ or −) with your answer.

2. Relevant equations
V=EPE/q, EPE=qEx=KE

3. The attempt at a solution
ΔKE/ΔV=q
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jan 29, 2013

### Staff: Mentor

Hi Rae_4, Welcome to Physics Forums.

Did you have a particular question about the problem? You seem to be on the right track with your attempt.

3. Jan 29, 2013

### Rae_4

Yeah. I'm trying that formula, but it keeps telling me my answer is incorrect. I'm not sure what I'm doing wrong. When I attempt the practice version it is trying to tell me the answer is times 10^-18 and nothing I have in that formula would give me a number that small. Are my formulas incorrect?

4. Jan 29, 2013

### haruspex

The energy is given in eV. The charge of an electron is 1.6021765 × 10 −19 coulomb. That's pretty small.

5. Jan 29, 2013

### Rae_4

Figured it out. Thanks!