If momentum were conserved in each collision, what would you expect the ratio of the total momentum before the collision to the total momentum after the collision to be? Youmay find a small difference between the momentum before and the momentum after the collision due to uncertainty in the measurements or a small external force on the carts during the collision (rolling friction, friction in the axles, or aslight angle of the track). Are there any of your collisions where momentum is not conserved? Is this expected?