Final answer:
In an elastic collision, both momentum and kinetic energy are conserved. Based on the collision behavior where cart B moves to the left after hitting cart A, we can deduce that cart A moves to the right, as expected in an elastic collision where one cart was initially at rest.
Step-by-step explanation:
If cart B collides elastically with cart A and subsequently moves to the left, this indicates an elastic collision has taken place. An elastic collision is one in which both momentum and kinetic energy are conserved. Since cart B was given a constant velocity and moves to the left after the collision, while cart A was initially at rest, we can conclude based on conservation of momentum that cart A must have moved to the right. Without further details, we cannot specifically determine whether cart A is hollow or whether the carts are truly identical; however, the information provided does suggest that the collision behaved as would be expected for an elastic collision between two objects, of which, at least initially, one is at rest