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Homework Help: Moving a charge/electrostatic force

  1. Jul 5, 2011 #1
    1. The problem statement, all variables and given/known data

    A point charge with charge q1 is held stationary at the origin. A second point charge with charge q2 moves from the point (x1,0) to the point (x2,y2).

    How much work is done by the electrostatic force on the moving point charge?

    Express your answer in joules. Use k for Coulomb's constant (k = 1/4*pi*epsilon.

    2. Relevant equations

    W = Uf-Ui = delta U
    k q1*q2/[(1/r2 - 1/r1]

    3. The attempt at a solution

    I don't know how to attempt when there are no q values and no r values. Please help.
  2. jcsd
  3. Jul 5, 2011 #2

    Have you worked through the problem using the variables that you were given? It may seem unnatural at first, but using variables instead of numerical values is good practice, especially for checking your work later on. This exercise appears to help you realize that.

    Also, your second relevant equation is not quite right. It might help to remember what the relation between the electrostatic potential and electric potential energy is.
  4. Jul 5, 2011 #3


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    Homework Helper

    You will have q1, q2, x2 and y2 in your final answer.
    You cannot get a numeric answer without knowing the numbers for those variables.
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