Can you add enough clay to the sled so that the propeller makes it reach a maximum velocity and then level off? What do the position and velocity graphs look like? This is called "terminal velocity". In what other situations is there a terminal velocity?

Try placing a different designs of wind shields or sails on your cart to affect its motion.

Add clay to the sled until it just won 't move. What 's the force on the cart at this moment?