Final answer:
The correct reason a rubber ball reverses direction upon bouncing off the floor is that the floor exerts a force on the ball (C). While momentum is conserved when considering the Earth-ball system, kinetic energy is not fully conserved as the ball deforms and loses energy to non-conservative forces.
Step-by-step explanation:
When a rubber ball dropped from rest bounces off the floor, its direction of motion is reversed because the floor exerts a force on the ball that stops its fall and then drives it upward. This interaction is what changes the ball's momentum. The answer to the student's question is (C) the floor exerts a force on the ball that stops its fall and then drives it upward. However, to address the loss of kinetic energy of the ball during the collision, the best explanation is that energy is required to deform the ball's shape during the collision with the floor, and energy was lost due to work done by the ball pushing on the floor during the collision.
Additionally, momentum changes due to the interaction with the floor, but when considering the ball and the Earth as a system, momentum is conserved. The Earth experiences an equal and opposite change in momentum in response to the ball's change in momentum, ensuring overall momentum is conserved. However, kinetic energy is not conserved in this inelastic collision, as the ball only reaches 90% of its original height after the bounce, indicating some energy was lost, likely due to non-conservative forces such as friction and sound.