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Homework Help: Conservation of Energy and electric potential

  1. Jun 13, 2005 #1
    The figure shows a graph of electric potential versus position along the x-axis. An proton is originally at point A, moving along in the positive x-direction. How much kinetic energy does the proton need to have at point A in order to be able to reach point E ( with no forces acting on the proton other than those due to the indicated potential)? How much kinetic energy does the electron need? Points B, C, and D have to be passed on the way.

    I don't have a copy of the graph, but

    A = 100 V
    B = 0 V
    C = -60 V
    D = -20 V
    E = 55 V

    Okay so I know that since positive charges move through decreases in potential, and the potential and potential energy are greatest at A, the proton will spontaneously travel from point A to point E. So, Ka = 0.

    But I'm really not sure how to calculate the kinetic energy for the electron. If someone could help me out, I'd appreciate it!!!
  2. jcsd
  3. Jun 13, 2005 #2

    Doc Al

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    Staff: Mentor


    Realize that the electron needs enough initial energy to get past each intermediate point. How much energy is needed to get to B? (Measure the KE in electron volts; once you get your final answer you can convert units if you wish.) Is that enough to take it to C? Etc. (Hint: To the electron, a negative potential difference represents a barrier. What's the steepest barrier (lowest potential) that the electron must overcome?)
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