In a lab, two identical lab carts (m = 1.0 kg) travel toward each other, each with a speed of 2 m/s. The cars collide, and one cart moves to the right with a speed of 3 m/s and the other moves left with a speed of 2 m/s. What best explains the results of the experiment? This experiment did not occur in a closed system. This proves the conservation of momentum since pi = pf . An additional mass was added to one cart, which explains the increase in speed. The increase in speed was due to the kinetic energy from one cart transferring to the other.