A student performs an experiment in which a 4kg object travels across a horizontal surface with an initial speed velocity of 6m/s and a 2kg object travels across a horizontal surface with an initial speed velocity of −3m/s. The objects travel toward each other and collide. Data collected from the experiment were used to create the velocity versus time graph shown that contains information about both objects before and after the collision. The positive direction is considered to be to the right. Which of the following statements are true regarding the data from the experiment? A- Both objects always travel in the positive direction during the experiment.

B- Kinetic energy is conserved during the experiment.

C- The position of the center of mass of the system remains constant during the experiment.

D- The velocity of the center of mass of the two-object system remains constant during the experiment.