I have to make a car type of thing out of a mousetrap any ideas on how?

I have to make a car that can travel 8 feet with out my pushing it, no ram, no water, no air i can only set it off. Once it hits the wall it has to send a ball over the wall which is 2 ft high then the car has to bounce back at least 1 foot, all in that order. It has to use it own connect energy i can use pretty much anything besides electric, motorized things and water air an fire, any ideas on how i can make this? it should be with in 10in to 14in length.