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Homework Help: Equation for speed of charges (electrostatics)?

  1. Feb 1, 2013 #1
    I am trying to do an exercise but there's no equation in the book that links speed and charges. Can anyone help? This is the exercise:
    1. The problem statement, all variables and given/known data
    There is a particle with mass = 20 grams and charge = 6 x 10^(-6) C, and another particle with mass = 50 grams and charge = -4 x 10^(-6) C. The distance between the particles is 1 m. Find the speed of each particle when their distance becomes 0.5 m.
  2. jcsd
  3. Feb 1, 2013 #2


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    Science Advisor
    Homework Helper
    Gold Member

    Not directly, but I'm sure you have equations that relate charge and distance to force, force and mass to acceleration, acceleration and distance to speed.
  4. Feb 1, 2013 #3
    Yes I tried using coulomb's law to find the force, and then each of the accelerations (a = F/m) but to find the speed from this (v^2 = 2*a*d) I need the individual distance traveled by each particle, and I only have the sum of both distances (0.5 m).

    Edit: And since the force has different value for different positions of the particles, doesn't that mean that the acceleration isn't constant? How can I find the speed using a non-constant acceleration?
    Last edited: Feb 1, 2013
  5. Feb 1, 2013 #4


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    Staff: Mentor

    In such cases it's often profitable to consider the problem in terms of conservation laws :wink:
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