From the question, we were made to understand that the collision between the two billiard balls was an elastic collision. Hence, an elastic collision is one in which the kinetic energy is conserved. Meaning the kinetic energy before the collision is still retained after the collision.
Kinetic energy before collision = kinetic energy after collision
B. A hypothesis is just an idea. And can become a Theory if there is some evidence. However a Theory is not a law, but an idea with supportive evidence
