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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

    haruspex

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    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

    gneill

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