posted by Joe .
Two lumps of clay having equal masses and speeds, but traveling in opposite directions, collide and stick together. Which of the following statements about this system of lumps must be true?
A. The momentum of the system is conserved during the collision.
B. The kinetic energy of the system is conserved during the collision.
C. The two masses lose all their kinetic energy during the collision.
D. The velocity of the center of mass of the system is the same after the collision as it was before the collision.