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Homework Help: Coulomb's Law and Net Force

  1. Jan 28, 2008 #1
    1. The problem statement, all variables and given/known data

    Two point charges lie on the x-axis. A charge of +7.7 uC is at the origin, and a charge of -4.4 uC is at x = 10.0 cm. At what position x would a third charge q3 be in equilibrium?

    2. Relevant equations

    F = k(q1)(q2)/r^2

    3. The attempt at a solution


    This was how I set up my diagram, and then I set F13 = F23.

    F13 = k(q1)(q3)/x^2
    F23 = k(q2)(q3)/(0.1-x)^2

    k and q3 cancels out, so it becomes

    q1/x^2 = q2/(0.1-x)^2
    (7.7e-6)/(0.1^2) = (4.4e-6)/(0.1-x)^2

    I got a final answer of 0.0244 m for x, or 2.44 cm. But it's not the right answer. What am I doing wrong? x__x
  2. jcsd
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