Two identical carts are held at rest. Between the two carts is a compressed spring of negligible mass. When the carts are released, the spring expands and the carts move in opposite directions. Which of the following statements is not true? I. Total momentum of the system is conserved. II. Kinetic energy of the system is conserved. III. Total mechanical energy of the system is conserved. _II and III only _II only _I only _III only _I, II, and III What is the answer? I thought it was only III since the velocity changes. However choosing only III was marked wrong.