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Coulomb's law charge

  1. Feb 19, 2010 #1
    1. The problem statement, all variables and given/known data
    two pith balls are suspended on a wooden dowel and have the same origin point. the two balls are push away from each other and are equally negatively charge. the string have the lenght L and the two strings form angle (theta).


    Fg= Gm1m2/r^2

    Fe= kq1q2/r^2

    2. Relevant equations
    using the electrostatic constant k dervie the formula below.

    Q= 2Lsin(theta) x square root of [mgtan(theta)/k]

    3. The attempt at a solution

    i found out that Fe= mgtan(theta) and Fe -Ft is the horizontal component. then i dont know wat to do after.
  2. jcsd
  3. Feb 21, 2010 #2
    Good Afternoon dom192,

    This is a statics problem. You need to draw a precise picture of the problem, then isolate one of the pith balls, and apply Newton's 2nd postulate for static equilibrium,
    Fnet = 0. These two equations will then allow you to solve for the unknown Q.

    To get you started, here's a picture:

    http://img109.imageshack.us/img109/6382/estatics1.jpg [Broken]
    Last edited by a moderator: May 4, 2017
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