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Homework Help: Electric charge/Colombs law problems

  1. Sep 9, 2011 #1
    I have a problem im working on before the end of today and I am having some trouble getting the right answer. What am I missing?

    1. The problem statement, all variables and given/known data
    The charges and coordinates of two charged particles held fixed in an xy plane are q1 = 3.11 μC, x1 = 5.72 cm, y1 = 0.703 cm and q2 = -6.23 μC, x2 = -1.59 cm, y2 = 2.45 cm. At what (a)x and (b)y coordinates should a third particle of charge q3 = 5.06 μC be placed such that the net electrostatic force on particle 2 due to particles 1 and 3 is zero?

    2. Relevant equations

    3. The attempt at a solution
    q1=3.1 E-6 x:0.0572 m y:0.00703 m
    q2=-6.23 E-6 x:-0.0159 y:0.0245 m
    q3=5.06 E-6

    First I find F1,2 for the x component:
    note:d=-0.0159 - 0.0572

    Next I conclude for equilibrium @q2 q1x=q3x. Same for y component.

    So to find X of q3...
    F1,3x ==> F1,2x= kq1q3/x2

    I assumed solving for X will give me the answer but its incorrect...
    Similar process for the y component.
  2. jcsd
  3. Sep 10, 2011 #2
    A thing to say--There's a much shorter method for this.You know the center of mass of system is point where all forces due to mass is zero.Same we can apply here as center of charge(though this method works BUT IT IS NOT OFFICIAL.DON'T USE THIS IN YOUR EXAMS) with same formula as center of mass just by replacing mass by charge(m1 by q1).
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