Objective: To build a device that will transport a 1 kilogram mass a distance of 10 meters using the energy released as the mass falls a distance 10 centimeters. Rules: 1. The only source of energy that may be used to move the vehicle is a 1 kg mass falling 10 cm. 2. All parts of the vehicle, including the 1 kg mass, must stay together for the entire trip 3. After the vehicle begins to move, it must be self-guided. I thought of using a pulley connected to an axle (with string pulling the 1 kg mass down on the pulley), but I don't know 1) how to connect a pulley to a cart-like-thing, 2) what materials to use to be lightweight, and 3) how to release the string without it rewinding like a yo-yo. I thought of using CD's for the 4 wheels. I don't know what would be an effective axle, though. Also I thought of using an empty spool for the reel part of the pulley. Now it's a matter of attaching the reel to some sort of construction to hold UP the mass. If anyone could help, I'd appreciate it! Thank you!