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Homework Help: Excess electrons question

  1. Feb 2, 2008 #1
    1. The problem statement, all variables and given/known data
    My problem states that a pith ball hangs at 20 degrees from the verticle and weighs 3 grams. It is moved 10cm by a charged rod. They both have the same charge. It asks what is the charge on the ball in C and approximatley how many excess electrons are on the ball.

    2. Relevant equations
    I have the equation kqq/rsquared

    3. The attempt at a solution
    I found all the sides to the triangle and I do not know where to go from there. I do not know the charges so how can I use the equation with q in it?
  2. jcsd
  3. Feb 2, 2008 #2

    Tom Mattson

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    10 cm in which direction? x? y? other? And where is the rod in relation to the ball? Is the charge distributed over the entire rod, or is it concentrated at a point?

    Did you draw a free-body diagram and set up the equations from Newton's second law? You should have 2 equations in 2 unknowns (q and the tension T in the cord from which the ball hangs).
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