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Homework Help: Find charge due to two particles

  1. Aug 30, 2008 #1
    Suppose that the magnitude of the charge on the yellow sphere is determined to be 2q and at (d2cos(theta), -d2cos(theta). Calculate the charge q_red on the red sphere at (d1,0) with a positive blue sphere,q, at the origin and whose net force,F, is in the direction of -y. The yellow sphere is negative and the red sphere is positive. ( See picture bellow)
    Express your answer in terms of q, d1,d2, and theta.

    Well the Fx on blue due to the yellow sphere= k(2q)(q)/(d2cos(theta))^2
    and the Fx on blue due to the red sphere = - k(q_red)(q)/(d1)^2

    Now what? I am unsure as to what to do now. Any help would be appreciated.

    Thank you.

  2. jcsd
  3. Aug 30, 2008 #2
    Would you set them equal to each other?
  4. Aug 30, 2008 #3
    I would? because of the fact that there is no net force along the x axis. Hence all x components of the force must cancel out to equal 0. Do you not get the right answer by doing that?
  5. Aug 31, 2008 #4
    I set them equal to each other and solved for q_red and got:

    q_red= 2qd1^2/(d2^2)(cos(theta)^2)

    Did I set up the original equations correctly? And did I find q_red correctly in terms of q, d1,d2, and theta?

    Thank you. I really appreciate the help.

  6. Aug 31, 2008 #5
    I have to turn this in soon so any help would be appreciated.

    thank you.

  7. Aug 31, 2008 #6
    I don't see anything wrong with it. Does anyone else see anything wrong with it?
  8. Sep 1, 2008 #7
    Does everyone agree with nova-ex? Are my equations correct?
  9. Sep 1, 2008 #8
    Not to be a bother but I have to turn this in tomorrow. So if you can please tell me whether or not I set the problem up correctly and got the correct formula for q_red: q_red= 2qd1^2/[(d2cos(theta))^2]?

    Thanks I would really appreciate it.

  10. Sep 2, 2008 #9
    Any opinions????
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