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Coulumb's Law

  1. Feb 9, 2006 #1
    I'm working on the following problem:

    A small spherical insulator of mass 9.00 x 10-2 kg and charge q1 = +0.400 µC is hung by a thin wire of negligible mass. A charge q2 = -0.700 µC is held 0.150 m away from the sphere and directly to the right of it, so the wire makes an angle with the vertical (see the drawing).

    http://www.boomspeed.com/boogiel80/hmwk18colulumb.gif [Broken]

    (a) Find the angle

    b) Find the tension in the wire.

    I figured out that the force that pulls between the two masses is around 1.12 x 10-1N. But after that I'm not sure where to go. I don't see how I can solve this problem using vecotor components (that is what I'm assuming I have to do). Also what does mass have to do with this problem? Does it have something to do with the tension? I normally can at least start problems, but this one I'm a little lost on.
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Feb 9, 2006 #2
    Think of what other forces there are in this system. It's not only the Coulomb force, there is another force which takes into account the mass. Which one is it? If you can get it, you can then use vector components to get the answers. Hopefully this will help.
  4. Feb 10, 2006 #3


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    Gold Member

    What force depends on mass?
    Draw a free body diagram were you break all the forces into 2 components - the x and the y axises. You get two equations (one for each axis). With that you can find the two unknowns.
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