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General question about solving force maximization problems

  1. Jun 19, 2010 #1
    I'm doing this E&M problem for fun (I'll be taking the class this fall), but now it's just starting to get frustrating. I can't really post the problem because there is a diagram, but I'm not really looking to be given the actual solution anyway, so I'll describe it to you:

    Two positive charges on the y-axis are acting on a single positive charge on the x-axis. The problem asks me to determine the x-position at which the single positive charge experiences the maximum force. I derived an expression to describe the superposition of the two positive electric forces on the single positive charge; then, to maximize it, I differentiated it, set it equal to zero, and solved for "x".

    My answer does not match the answer in my textbook, but I can't think of any other way to do this problem; I always assumed that maximization was straightforward. So, could someone please point me in the right direction, conceptually? Thanks.
     
  2. jcsd
  3. Jun 19, 2010 #2
    Did you take the vector sum and maximize its magnitude, or did you ignore how each charge provides a force in a different direction?
     
  4. Jun 19, 2010 #3
    Two on y axis, and one on x axis.
    So, the position is on the x axis. Please thinking again.
     
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