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Electric Forces

  1. Sep 13, 2013 #1

    dwn

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

    Two point charges are 3 m apart and their combined charge is 20µC. If they
    repel each other with a fore of 0.075 N, what are the two charges? Ans: 15 μC and 5μC  

    2. Relevant equations

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

    (could someone mention in their response how we use the math text in our posts, so that I can make it more convenient for the reader)

    3. The attempt at a solution

    I'm really not so sure where to begin here, but I made a few attempts by manipulating both q2 and q2. I will post one of them below:

    9*109 (q1+q2)/32=0.075N
     
  2. jcsd
  3. Sep 13, 2013 #2

    Doc Al

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    Staff: Mentor

    Good.

    Check out the FAQ, under "SITE INFO/Frequently Asked Questions" at the top of every page.

    The one mistake you made was to use q1+q2 instead of q1*q2.

    The second equation you'll need is q1+q2 = ??
     
  4. Sep 13, 2013 #3

    dwn

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    I tried that in one of my attempts, but I don't see the "bridge" between the two equations.

    If I solve Coulombs equation for q1*q2, I don't see where I'm supposed to plug in q1+q2 = 20 into the other equation....?
     
  5. Sep 13, 2013 #4

    Doc Al

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    Staff: Mentor

    You'll have two equations and two unknowns. Solve them simultaneously, using any method you like. (Such as substitution.)
     
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