Try other collisions: one cart moving and the other standing still; both moving in the same direction, one fast and one slow; both moving toward each other, one fast and one slow. In each case, make a prediction about the final velocities and then compare the results to your prediction.

Try collisions between carts of different masses. First record the force on each. Are the forces the same? Then record the velocity of each. How did the change in forces and velocities after the collisions for carts of different masses compare to the forces and velocities after the collisions for carts of the same mass?