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Homework Help: Coulomb's Law (should be easy)

  1. Jun 3, 2008 #1
    1. The problem statement, all variables and given/known data
    Two equally charged particles are held 3.2*10^(-3)m apart and released from rest. The initial acceleration of the first is 7 m/s^2 and that of the second is 9 m/s^2.

    If the mass of the first is m1= 6.3*10^(-7) kg, what are a) the mass of the second particle and b) the magnitude of the charge of each?

    2. Relevant equations


    3. The attempt at a solution

    I just need a kick in the right direction here. I am looking at a worked solution to the first part and they make the assumption

    F1=F2 , thus, m1a1=m2a2

    But, for some reason I am uneasy with this. Why are these two forces equal?

    Sorry for the lame question... I am out of practice and am trying to do some review.

  2. jcsd
  3. Jun 3, 2008 #2


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    They form an action-reaction pair (Newton's third law). They must be equal!
  4. Jun 3, 2008 #3


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    F = q1q2 /r^2

    q1q2 is the same for both particles, as is r.
  5. Jun 3, 2008 #4
    I guess I can live with that.
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