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College Physics II Charge/ Coulombs Law

  1. Aug 25, 2011 #1
    1. The problem statement, all variables and given/known data
    A point particle that has a charge of 14.5 µC is located at x = 0, y = 0 and a point particle that has a charge q is located at x = 11.6 cm, y = 0. The electric force on a point particle that has a charge of 5.8 µC at x = 23.2 cm, y = 0 is -(19.7) N ihat. Determine the charge q.

    2. Relevant equations
    F = (k*q1*q2)/d^2

    3. The attempt at a solution

    -19.7 = ( 9e9 * 5.8e-6 * q ) / (.112^2)

    F = ( 9e9 * 14.5e-6 * 5.8e-6 ) / (.232^2)

    not sure what to do to solve this. Help fast please. Due in 1 hr
  2. jcsd
  3. Aug 25, 2011 #2
    there will be two equations...
    F=(9e9*5.8e-6*q)/(.112^2) that is the force between first two charges
    -19.7=[(9e9*q*14.5e-6)/(.112^2)]+[( 9e9 * 14.5e-6 * 5.8e-6 ) / (.232^2)]

    i.e. the force b/w last two charges
    this last equation gives you the charge n first equation eventually leads you to force on first charge.
    Last edited: Aug 25, 2011
  4. Aug 25, 2011 #3
    From what you said the charge from the second equation, I got q = -3.25e-6 and that is also not the correct answer. I dont need to be solving for force between any of the charges.

    Any thing else?
  5. Aug 25, 2011 #4


    User Avatar

    Staff: Mentor

    The y-coordinates of all the charges are zero, so the charges all lie along a single line, the x-axis, and you won't have to deal with any trigonometry :smile:

    The charge q lies to the right of both the other charges, so writing a single equation for the force exerted by the other two should be straightforward. To begin with, write the equation symbolically and don't plug in any numbers until you've solved for the appropriate variable.

    Since you're interested in the force exerted on the rightmost charge by the other two it would be helpful to know the distances between that charge and the other two. What are they?
  6. Sep 9, 2011 #5
    may i knw the correct answer???
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