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Total energy when potential graph is given

  1. Jan 25, 2013 #1
    Total energy when positions vs time graph is given

    1. The problem statement, all variables and given/known data
    24fznys.png

    (answer: -5J)

    2. Relevant equations
    energy initial = energy final

    3. The attempt at a solution
    At the crest of each wave, the particle has only potential energy, and at the middle of each wave the particle has only kinetic energy, and these values are equal. By looking at the slope when the graph crosses the horizontal axis, you can determine that it travels at 5m/s then. After this point, I do not know how to continue.
     
    Last edited: Jan 25, 2013
  2. jcsd
  3. Jan 25, 2013 #2

    tms

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    Disregard.
     
  4. Jan 25, 2013 #3

    ehild

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    You said the potential graph is given. Where is it?

    ehild
     
  5. Jan 25, 2013 #4
    I'm sorry, I mis-titled the post originally. The potential graph is not given, only the position vs time graph is given
     
  6. Jan 25, 2013 #5

    ehild

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    The motion looks SHM. But you need the mass of the particle.

    ehild
     
  7. Jan 25, 2013 #6
    I gave the entire problem. No mass was given, and nothing analogous to the spring constant was given. However, I think you can find the ratio of the two, as the period = 2π * sqrt(m/k) = 8. I don't see how that helps, though
     
  8. Jan 25, 2013 #7

    ehild

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    You also know the amplitude, A=5 m. The energy of the SHM is 1/2 kA2. You need the mass.

    You also need the zero point of potential energy. If it is SHM, the potential energy is zero at zero position, and it is never negative. Something is very wrong with the problem.

    ehild
     
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