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Electric Forces

  1. Oct 5, 2009 #1
    1. The problem statement, all variables and given/known data[http://img44.imageshack.us/img44/1104/58339946.jpg [Broken]][/URL]



    2. Relevant equations [F=k*abs(q1)*abs(q2)/r^2]



    3. I understand the equation, but I am having trouble with my signs and also how to include the distance in the equation. I know that the force can't be zero between the charges, and I think it has to be farthest away from the larger positive charge to make them equal to zero. The forces point in the same direction because they are opposite.]
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Oct 5, 2009 #2

    rl.bhat

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    Consider a point at a distance x from -q toward right, and find the forces on a unit positive charge due to two charges. Equate them to get the value of x.
     
  4. Oct 5, 2009 #3
    I don't understand what you mean by that... I think I'm over-thinking this.
     
  5. Oct 5, 2009 #4

    rl.bhat

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    Force on unit positive charge due to -q at a distance x*1o^-2 m from it is....?
    Force on unit positive charge due to 2q at a distance (10 + x)*10^-2 m is....?
    Since net force is zero, equate them to find x.
     
  6. Oct 5, 2009 #5
    Thanks very much, I got it now.

    ((k*q)/x^2)-((k*2q)/(x+10)^2)=0, solving for x gives 24.142cm. Accounting for the distance of 5cm on the x axis give the point to be 29.142cm. This was the correct answer. Thanks!
     
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