In trial 1 of an experiment, a cart moves with speed vo on a frictionless, horizontal track and collides elastically with another cart that is initially at rest. In trial 2, the setup is identical except that the carts stick together during the collision. How does the speed of the two-cart system's center of mass change, if at all, during the collision in each trial? Trial 2 Trial 1 Does not change (A) Does not change (B) Does not change (C) Decreases (D) Decreases Decreases Does not change Decreases