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Homework Help: Coulomb's law question

  1. Aug 18, 2015 #1
    1. The problem statement, all variables and given/known data
    The charge on two pith balls can be calculated by knowing their masses and observing the angle of separation between the balls.
    If both balls are equally charged and they are suspended by strings that are 1.0 m long, calculate that charge.

    2. Relevant equations
    F = k q Q / d^2

    3. The attempt at a solution
    ma=kq^2/d^2 (both q's are the same)
    Im a bit stuck here because i don't know how to find the acceleration. Thank you!

    Attached Files:

  2. jcsd
  3. Aug 18, 2015 #2


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    Homework Helper
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    The balls remain at rest.
  4. Aug 19, 2015 #3
    Why acceleration?

    Why don't you try equilibrium of forces?
  5. Aug 19, 2015 #4
    Have you drawn a free body diagram on either of the balls, or do you feel you have advanced beyond the point where you need to use FBDs?

  6. Aug 19, 2015 #5


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    Staff: Mentor

    This is not Fnet, because the electric force is not the only one acting on each ball. Your first step should be to choose one ball (either one will work, so you can toss a coin or something), then identify all the forces that act on it and draw a free-body diagram for it as Chet asked for.
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