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Homework Help: Force of weight of the suspended ball

  1. Nov 22, 2004 #1
    i kinda need help. okay im posting my question:
    Two pith balls have a mass of 1.0g and have equal charges. One pith ball is suspended by an insulating thread. The other is attached to a static insulator and is brought close to the suspended ball so that they are 5 cm apart when repulsion occurs. After repulsion, they come to rest such that both are at the same height above ground. The suspended ball is now hanging with the thread forming a 30 degree angle with respect to its former position. Calculate the following:
    1-Force of weight of the suspended ball.
    2-The force of repulsion between the two.
    3-The net charge on each.
    I have no idea how to find out the force of repulsion and the net charge. We can find the weight my using the W=mg formula. So i'm confused with that. I need help . Thank God i found this cool forum
    Last edited by a moderator: May 8, 2015
  2. jcsd
  3. Nov 22, 2004 #2
    The weight factor in the other parts isn't a simple W = mg problem. Try considering the force due to gravity as a torque and the repulsion from the other ball as a countertorque. I hope this gets you started.
  4. Nov 22, 2004 #3
    I didn't get it do you mean gravitational force by force due to gravity?
    i didnt get it :uhh: :uhh: :frown:
  5. Nov 22, 2004 #4
    The force due to the earth's gravity has components is what I'm referring to. These components can be broken up into components parallel and perpendicular to the line between the centers of the two balls. (namely mgcos(30) and mgsin(30)) If you set the force of gravity acting to push one ball toward the other and balance it with the repulsive force of the charge on the two balls you should find your answer. Clearer?
  6. Nov 22, 2004 #5
    Ys yes yes yes thank u thank u thank thanku :biggrin: :biggrin: :biggrin: :biggrin: :rofl: :rofl: :rofl: :biggrin:
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