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Getting work out of kinetic energy

  1. Apr 25, 2012 #1
    I am doing a presentation on energy as part of a class project.As part of the presentation I would like to physically demonstrate that the amount of work you can get out of a moving body (its kinetic energy) is equal to the amount of work you put in.I want to somehow take a moving body and get it to do a measurable amount of work that would be equal to its kinetic energy.This is turning out to be surprisingly difficult.I rigged a pinewood derby car so that I could supply a constant force over some set amount of distance.I tried running the car into a mass suspended on the end of the string and seeing how high the mass rose as a result but not all of the energy is being transferred to the mass (the car still has some velocity after impact).??Any suggestions would be greatly appreciated.
  2. jcsd
  3. Apr 25, 2012 #2


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    Gold Member

    Make sure that you get a plastic impact by having the car captured in your ballistic pendulum. Then you will have to account for the loss due to impact.
  4. Apr 25, 2012 #3


    Staff: Mentor

    Use a Newtons cradle.
  5. Apr 26, 2012 #4

    Philip Wood

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    Gold Member

    Hook a (weakish) spring on to the car as it's moving. Observe the maximum extension, x, (preferably by taking a rapid succession of pictures). Hope to find that
    [tex]\frac{1}{2}mv^2 = \frac{1}{2}kx^2.[/tex]
    Negligible energy dissipated in collision.
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