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Homework Help: Electric Force Question

  1. Jul 2, 2006 #1
    Here is the question that I have no idea what is happening

    "What is the change in potential energy of a particle of charge +q that is brougt from a distance of 3r to a distance of 2r by a particle of charge -q? "

    Here's what I tried

    -W = deltaU
    W = qEd
    W = (kq1q2/r^2) d
    d= 3r - 2r = r

    substituting I get
    W = kq1q2/r
    so deltaU = -kq1q2/r..............im correct up to here, but its not the final answer according to the book,....the explaination then shows some weird things that I dont understand.

    but isn't the question asking for change in potential
    so shouldn't deltaU (-kq1q2/r) be the answer???
    Last edited: Jul 2, 2006
  2. jcsd
  3. Jul 2, 2006 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Hint: The potential energy of two charges separated by a distance r is given by kq1q2/r (where the zero level is taken to be at r = infinity).
  4. Jul 2, 2006 #3
    [nvm i get it now]
    I have another problem though
    Last edited: Jul 3, 2006
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