# Getting work out of kinetic energy

1. Apr 25, 2012

### cdot

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. Apr 25, 2012

### OldEngr63

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.

3. Apr 25, 2012

### Staff: Mentor

Use a Newtons cradle.

4. Apr 26, 2012

### Philip Wood

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
$$\frac{1}{2}mv^2 = \frac{1}{2}kx^2.$$
Negligible energy dissipated in collision.

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