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Homework Help: ElectroStatic Equilibrium problem

  1. Sep 8, 2011 #1
    1. The problem statement, all variables and given/known data
    particle 1 of charge q1 (at origin) and particle 2 of charge q2 = 3q1, are held at separation L on an x axis. If particle 3 of unknown charge q3 is to be located such that the net electrostatic force on it from particles 1 and 2 is zero, what must be the (a) x and (b) y coordinates of particle 3?


    2. Relevant equations
    F=k|q1||q2|/d2


    3. The attempt at a solution
    I assumed q1 and q2 are like charges so I put q3 in the middle. This could be my mistake since im getting incorrect answers for x, I do know y = 0.
    If q3 does belong between the two charges on the X axis, then I am not setting up my d2 part of Coulombs law. Could someone point me to the right direction?
    Net Force = 0
    F31=k|q3||q1|/?2
    F32=k|q3||q2|/?2
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Sep 8, 2011 #2

    wukunlin

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    Gold Member

    if the particle is at distance d away from q1, what distance is it between the particle and q2? assuming this is a one dimensional problem
     
  4. Sep 8, 2011 #3
    Okay say, if distance between q3 and q2 =d than distance between q3 and q1 is L - d correct? So...
    kq3q1/(L-d)2=kq3q2/d2
    =>q1/(L-d)2=q2/d2

    If the above steps are correct... is it safe to assume to use the fact: q2=3q1 to eliminate the two charges?
     
  5. Sep 8, 2011 #4

    wukunlin

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    Gold Member

    yes :)
     
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