Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Electric potential energy and point charges problem

  1. Jan 28, 2007 #1

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

    Two point charges 2.0 cm apart have an electric potential energy -149.9 µJ. The total charge is 28 nC. What are the two charges?

    2. Relevant equations

    U = (kqQ) / r

    3. The attempt at a solution

    U = -149.9 x 10^-6 = [(9 x 10^9)(28 x 10^-9 - q)(q)] / (0.02). Is that correct? I seem to get the wrong answer.

  2. jcsd
  3. Jan 28, 2007 #2

    Chi Meson

    User Avatar
    Science Advisor
    Homework Helper

    This appears to be a simulateous equation problem. You don't know what either charge is, but you do know that the sum of both charges is 28 nC. (If I understand the problem correctly).

    Since the PE is negative, that means one charge is + and the other is -. Therefore, how much more is the + charge's magnitude greater than that of the negative?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook