# Velocity of a body on a slope

1. Dec 11, 2012

### Jonnyc0213

Hi guys new to the forum - sorry if I'm not as advanced as you lot :tongue2: I'm currently only at A Level in my adventures of Physics!
(I didn't think this would fall under homework help, I apologize if it does)

Anyway, tomorrow in school there is a house technology project, and I've been entered without doing this as a subject. I think I'll do it anyway since I do Physics.
Anyway - we have to build a small car, it is then released from rest, at the top of a slope onto a ramp. The car that goes the furthest wins. (I'm going to assume the angle is 30°)

Does anyone have any equations that could help me work out how to achieve the maximum distance? Or even any tips on the structure of the car?

I know how to do projectile motion of course, but how can I maximize the velocity at the end of the ramp?

Any help will be greatly appreciated - I'm at a huge disadvantage tomorrow and I want to make a good account for myself! Thanks guys!

2. Dec 11, 2012

### K^2

If you ignore inertia of the wheels, the speed at the bottom of the ramp will only depend on friction/weight ratio. Less friction/weight, more speed. That simple. So you need to either make your car heavier or reduce friction. Drag will depend only on shape of the car and speed, while friction in wheels will depend primarily on weight.

All in all, heavier car will probably do better, because it will help you ignore air resistance.

Now onto inertia of the wheels. It will slow your car down at the bottom, but all that energy doesn't disappear. It is still stored in rotation of the wheels. So the car will carry extra distance afterwards thanks due to the same inertia. Since your car is moving slower overall, you would have less drag. So I would recommend making wheels as massive as possible, keeping in mind that you want the weight nice and balanced. If you have time to get creative, you might even consider building a flywheel that spins at higher RPM than the wheels. That will let your car go really slowly, build up a lot of inertia in the flywheel, and use that to travel the distance, while other cars waste energy on fighting drag. Of course, if you build too much resistance into your belt/gear system, that will cost you all of the advantage, so simpler might be better here.