Build a car that can hold a sail.
The sail is to cause drag and slow the car down.
To test: 1. Set the car off the starting contraption without the sail.
2. Mark the point the front wheel touches the floor.
3. Set the car off the starting contraption with the sail.
4. Measure the distance the from where the front wheel touches the
floor to the first mark
to get the difference between the two runs.
The winner is the car with the greatest difference.