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Homework Help: Coulomb's law (place charge so it has no net force) - only have 2 hours, help please!

  1. Jan 23, 2012 #1
    1. The problem statement, all variables and given/known data

    A charge, Q2 = -7.00x10^-6 C, is 8.00 cm to the right of charge Q1 = 6.00x10^-6 C. Where can a third charge be placed, along the line connecting Q1 and Q2, such that it experiences no net force? Give distances relative to Q1 and use a plus sign if the third charge is to the right of Q1

    2. Relevant equations


    3. The attempt at a solution

    I did q1/x^2 = q2/(x+0.08)^2 and solved for x. I got a quadratic which gave me roots 0.998459 and -0.0384593. This is assuming that the order is Q3 then Q1 then Q2.

    If I do it with the order as Q1 - Q2 - Q3, then I get two negative roots (the more negative one still matches up with 0.998459 if I take into account the 0.08 between Q1 and Q2).

    So, would my answer be -0.998459 m because Q3 is to the left of Q1 and the question said to make it positive is Q3 is to the right? I have one try left to get this right, but I'm not confident this is correct.
  2. jcsd
  3. Jan 23, 2012 #2
    Re: Coulomb's law (place charge so it has no net force) - only have 2 hours, help ple

    Looks right to me.
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