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Homework Help: Easy electro charge question, calculation error?

  1. Feb 5, 2012 #1
    1. The problem statement, all variables and given/known data

    The sum of two point charges is + 11μC. When they are 2.9 cm apart, each experiences a force of 194 N. Find the charges given that the force is:
    (In micronewtons)

    2. Relevant equations
    F = KqQ/r^2
    q + Q = Net charge

    3. The attempt at a solution
    I confirmed this with my friend and he got the same answer as me, so maybe we are both making the same mistake.

    q + Q = 11 => q = 11 - Q
    F = kq(11-Q)/r^2 => 194 = (9x10^9)(11-Q)Q/(0.029)^2
    After solving and simplifying the quadratic I got Q = 11 and 1.6*10^-12 which is wrong.
  2. jcsd
  3. Feb 5, 2012 #2


    User Avatar

    Staff: Mentor

    Welcome to PF, Paulkaryote.

    What happened to the units attached to the charge? They were not Coulombs, but microcoulombs.
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