Elastic and Inelastic Collisions Practice Test

Two carts collide on a horizontal track. They bounce apart, and measurements show the system’s total kinetic energy decreases. Which statement must be true about the collision?

Cart $A$ collides with cart $B$ on a frictionless track. The collision is described as elastic. Immediately after, the carts separate and the total kinetic energy of the two-cart system is unchanged.

Which statement is correct for the two-cart system?