You are given two carts, A and B. They look identical, and are made of the same material. You place A at rest on an air track and give B a constant velocity directed to the right so that it collides elastically with A.

After the collision, both carts move

to the right, the velocity of B being smaller than what it was before the collision. What do you conclude?

BLUE: Cart A is hollow.

YELLOW: The two carts are identical.

PINK: Cart B is hollow.

PURPLE: need more information