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Homework Help: Need help with force of electricity

  1. Feb 8, 2008 #1
    1. The problem statement, all variables and given/known data
    Four charged particles are placed so that each particle is at the corner of a square. The sides of the square are 17 cm. The charge at the upper left corner is +4.0 µC, the charge at which the upper right corner is -5.0 µC, the charge at the lower left corner is -2.9 µC, and the charge at the lower right corner is -9.1 µC.

    a) What is the magnitude of the net electric force on the +4.0 µC charge? (In Newtons).

    b) What is the direction of this force (measured from the positive x-axis as an angle between -180 and 180, with counterclockwise positive? Answer in units of degrees.

    c) What is the magnitude of the net electric force on the -5.0µC charge? (Answer in units of Newtons.)

    2. Relevant equations

    The Coulomb constant is 8.98755 x 10^9 N.

    3. The attempt at a solution

    I hope I posted this correctly, if not, I'm sorry for the trouble!

    Thanks so much for the help, I've been trying to figure this out for days and just don't get it....There's another part to the problem that I might need help with, but I have to figure this part out first.
  2. jcsd
  3. Feb 8, 2008 #2
    Start by drawing all four charges and then draw a force diagram for the charge of interest. You will probably find that you run into a bit of trigonometry.
  4. Feb 8, 2008 #3
    But what equations should I use? (Other than trigonometry functions)
  5. Feb 8, 2008 #4
    Start with F = kQq/(r^2)
  6. Feb 8, 2008 #5


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    Homework Helper

    |F|=k*q1*q2/r^2 and the fact that F is directed along the line between the two charges. Show us how you computed the force of ONE of the other charges on the +4 charge. That's good place to start. The forum helps those who help themselves.
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