Force-Weight Pinewood Derby Car.

I'm trying to make a fast derby car. I was wondering if I could make a car that can drop/eject weight once it comes off of the incline. Would that increase speed or would it make it slower?

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    $\begingroup$ Would it make it legal? $\endgroup$ – DJohnM Jul 9 '13 at 23:13
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    $\begingroup$ For the uninformed, it might be useful if you give a short description of what "Pinewood Derby" is... $\endgroup$ – Kyle Oman Jul 9 '13 at 23:30
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    $\begingroup$ This question appears to be off-topic because it is about an engineering problem. We deal with specific physical concepts. $\endgroup$ – user10851 Jul 10 '13 at 14:23
  • $\begingroup$ So where do people go to ask engineering problems? That is not to correct reason to close the question. Maybe in can be closed based on the quality of the posting, but not on the subject matter. $\endgroup$ – ja72 Jul 10 '13 at 18:17

The extra weight is going to be carrying some forward momentum and inertia with it, so rolling resistance and friction that slow down the car will have less work to do to slow the car down, once it's lighter. Then again, the car will be lighter so there will be less rolling resistance and friction. You'd really have to do the calculation of your particular setup to see which term dominates.

If you "eject" the mass, then conservation of momentum dictates that you can gain or lose velocity depending on which direction you eject it.


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