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Electric Forces; Coloumb's Law question

  1. Dec 10, 2006 #1
    1. The problem statement, all variables and given/known data
    three spheres, each with a negative charge of 4.0 X 10^-6 C, are at the vertices of an equilateral triangle whose sides are 0.20m long. Calculate the magnitude and direction of the net electric force on each sphere.

    2. Relevant equations

    Fe= kq1q2/r^2, where k is the constant, k=9.0 X 10^9 N*m^2/C^2

    3. The attempt at a solution

    i plugged in the values..but I don't seem to be getting the answer. There are 2 forces acting on each of the spheres, right? the answer is 6.2N
  2. jcsd
  3. Dec 10, 2006 #2


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    Saying "I plugged in" is not telling us what you did. Yes there are two forces acting on each charge. How are they acting? How did you combine them?
  4. Dec 10, 2006 #3
    since Fe=kq1q2/r^2
    Fe= k*(4.0 X 10^-6C)^2/ (0.20m)^2
    Fe= 3.6N

    how are they acting? they are supposed to repel each other, but i don't understand how that would affect the magnitude of the force. To combine them, i think i have to add 3.6N + 3.6N..but that isn't working. What do you think?
  5. Dec 10, 2006 #4


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    I think you need to remember that forces are vectors and need to be added as directional quantities. I did not check your numerical calculation, but I expect the vector addition is your problem.
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