How do you get a mousetrap car to go forward and then backward?

clphysics

I have a physics project and my mousetrap car has to go forward seven meters and then back seven meters. I can only use two mousetraps.

A.T.

Use the mouse traps as catapults to shoot some mass horizontally, so the kick back accelerates the car. The second trap is opposed to the first, and fires when the car hits a wall 7 meters away.

Molydood

Use a 7m long piece of string that wraps itself around a bobbin connected to the wheels. When the string is pulled all the way onto the bobbin it pulls out a pin to activate the second mouse trap. The bobbin size can be worked out through trial and error unless you want calculate the changing diameter matched to wheel size !

A.T.

Speaking of strings. It might be more effective to use a string to translate the energy stored in the spring to the wheels, than the back kick approach.