# Electrical potential energy: 3 charges in a line

1. Feb 11, 2009

### alicemunro

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

A positive charge, q1 is at (-20cm,0). An equal and opposite charge q2 is at (20cm, 0). A positive charge q3, equal to q1, is placed at (60cm,0). What is the potential energy of the three charges??

2. Relevant equations

EPE= kq / r

3. The attempt at a solution
EPE = k( (5 X 10^-9)/.2) + (5 X 10^-6)/.6) - (5 X 10^-6)/.2))
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Feb 11, 2009

$$U = k \frac{q_a q_b}{r_{ab}}$$