Physics project: Self propelled car

[Arix]

ok, so i have a physics project. we were assigned to use a mouse trap tied to the axle by a string to propel a homemade car of sorts. but he says we can use and propulsion system as long as it doesn't use combustion or electricity. i don't want to use a mouse trap and I'm looking for other ideas. maybe magnetic? any ideas? we also are to design a braking system so that the car will stop at a self-set distance such as 40m. any ideas?

 

[mgb_phys]

What about a mouse?

 

[Arix]

cant be animal powered either