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Homework Help: Coulomb's Law and acceleration

  1. Jan 20, 2012 #1
    1. The problem statement, all variables and given/known data

    Two very small 8.55-g spheres, 15.0 cm apart from centre to centre, are charged by adding equal numbers of electrons to each of them. Disregarding all other forces, how many electrons would you have to add to each sphere so that the two spheres will accelerate at 25.0g when released?

    2. Relevant equations

    F= abs( (kq1q2)/r^2)

    3. The attempt at a solution


    (245)(0.15)^2 = (9.00x10^9)(x^2)
    (5.51 / 9.00x10^9) = x^2
    2.47x10^-5 C = x = charge of one sphere

    (2.47x10^-5) / (1.6x10^-19) = 1.55x10^14 electrons in one sphere

    The answer's wrong :(
    Last edited: Jan 20, 2012
  2. jcsd
  3. Jan 20, 2012 #2


    User Avatar

    Staff: Mentor

    You've used acceleration ("245") where you need force. What force is required to produce the acceleration 245 m/s2?
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