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Homework Help: Need help - about Coulomb's Law and SHM

  1. Nov 23, 2006 #1
    need help -- about Coulomb's Law and SHM

    Two positive charges +Q are held fixed a distance d apart.
    A particle of negative chage -q and mass m is placed midway between them, then is given a small displacement perpendicular to the line joining them and released. Show that the particle describes simple harmonic motion and find the period.
    i've found that the net force acting on the -q is
    F = - (qQd) / [4(pai)(z)(y^2 + (0.5d)^2)]^(3/2) = ma
    where z is the permittivity, and y is the displacement of -q

    how i can show that a = - w^2 y?
  2. jcsd
  3. Nov 23, 2006 #2


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    Well, you need to redo the calculation of the total net force.

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