Fastest cart ever!!

In science we have been given a team challenge to make a cart And the idea we came up with was to make a cart using a plastic bag and a piece of card board and guess what we had the fastest car in the world.when we tested our car is the best in the class and we came first.The things things we focused on was friction, force and how to make it unbalanced.What the struggles were in our was thinking of our way to make the cart go fast.But then I came up with the idea to make a plastic back cart.