Science Buddies: "Ask an Expert"

All though the title sounds easy its very misleading the Point of the Project is to make a "Car" that cant be bigger then 20cm X 25cm X 40cm. then make it roll down a 3 meter incline thats at 30 Degrees and to top it off have it stop on a line that is 3 meters away from the end of the incline. and I need help with this
thinking of using a Pine wood derby car kit to make the car but any ideas on how to build it to do the task?

Pinewood derby sounds fine. If the wheels were pinned to the rear axle (the axle would have to turn), the axle could wind up some strong thread, the end of which was fastened to the car. when all the thread was wound up, the axle would have to stop turning , wouldn't it. If the thread was the right length, wouldn't the car stop on the line?