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Homework Help: Conservation of Energy

  1. Mar 2, 2008 #1
    [SOLVED] Conservation of Energy

    1. The problem statement, all variables and given/known data

    A proton (charge e, mass = 1.67 * 10^-27 kg) accelerates from rest by crossing a potential difference V = 3.00 V

    a.) Find the velocity v_0 it acquires?

    (Suppose this proton, having initial velocity v_0 from part (a), moves from very away directly towards a stationary heavy ion which is singly charged, i.e. having the same charge as the proton, +e.)

    b.) Find the distance r_min between the proton and the ion at the moment of closest approach?

    c.) Find velocity v of a proton when it is at a distance r = 2r_min from the ion

    2. Relevant equations

    a = (q/m)E

    V = kQ/r

    V = E*d (parallel plate)

    3. The attempt at a solution

    I am literally stuck for part a into determining what it could be, it seems something is missing in the problem.

    Please help.

  2. jcsd
  3. Mar 3, 2008 #2

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    What is the work done on a charge q when it goes from a point with potential V1 to a point with potential V2?
  4. Mar 3, 2008 #3
    work done is the change in potential energy so (V2 - V1)*q?

    I was wondering could I just integrate the equation a = (q/m)E into v = (q/m)*V? because electric field is the derivative of potential difference?
  5. Mar 3, 2008 #4

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    The change in KE is the work done. There's no need to integrate, since it is the potential difference which has been given.

    I feel you should go through the basics once more by yourself.
  6. Mar 3, 2008 #5
    I know change in potential energy = -Work

    and that change in potential difference is the potential-energy change per unit charge...
    so can't I just set Vq = U and then set that = (1/2)mv^2 and solve for v?
  7. Mar 3, 2008 #6

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    That's the correct way.
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