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Homework Help: Tension of a sting

  1. Jul 5, 2011 #1
    1. The problem statement, all variables and given/known data
    A small ball with a mass of 35 g and a charge of -0.1 µC is suspended from the ceiling by a string. The ball hangs at a distance of 5.0 cm above an insulating floor. If a second small ball with a mass of 85 g and a charge of 0.2 µC is rolled directly beneath the first ball, will the second ball leave the floor?

    ans: 0.415 N

    3. The attempt at a solution

    T of the ball
    T = mg = 0.035kg * 9.8 = 0.343 N

    F of two balls
    F = k * q1* q2 / (l)^2
    = 0.021576 N

    i am not sure what to do any hints?
  2. jcsd
  3. Jul 5, 2011 #2


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    Homework Helper

    0.415N? Isn't this a yes or no question?

    So gravity pulls the second ball down with 0.343N of force, whereas the other ball pulls it up with 0.022N. Do you think the ball will go up?

    By the way, I think you made a mistake in calculating the electrostatic force. It should be higher, although not high enough to change the answer.
  4. Jul 6, 2011 #3
    the answer is no opps
    there is a second part of the question about what the tension of the string is and i'm not sure how to get it
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