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Homework Help: Point charges on a line

  1. Jan 29, 2007 #1
    1. The problem statement, all variables and given/known data
    Two point charges lie on the x axis. A charge of +8.4 µC is at the origin, and a charge of -3.8 µC is at x = 10.0 cm.
    At what position x would a third charge q3 be in equilibrium?

    2. Relevant equations
    F=(kq1 q2)/r^2

    3. The attempt at a solution
    I think that my main problem was that I wasn't quite sure how to solve for the distance if I don't have the charge for the third particle or its relation to the other charges.
  2. jcsd
  3. Jan 29, 2007 #2
    Then, simply use q3 as the value each time you plug it into your relevant equation. It should cancel out later.
  4. Jan 29, 2007 #3
    I tried that, but the q3 doesn't cancel out and I don't know how to get rid of it because they don't state any relationships between the charges. (ex: q1=q, q2=-3q, etc.)
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