Question

A 1kg billiard ball strikes another ball with the same mass. If the first ball stops and the second ball then speeds away at 6m/s in a simple elastic collision, what was the speed of the first ball before it hit the second?

A) 3 m/s
B) 6 m/s
C) 9 m/s
D) 12 m/s

Answer 1

In an elastic collision where two objects of equal mass collide and one stops, the other object moves away with the initial velocity of the first object. In this case, the speed of the first ball before impact was 6 m/s. Therefore correct option is B

Step-by-step explanation:

The student's question asked about the initial speed of a billiard ball in a simple elastic collision. In the case where two objects of equal mass collide elastically and the first object comes to a stop after the collision, the second object must leave with the velocity that the first one had originally due to the conservation of momentum. Since the second ball speeds away at 6 m/s, this must have been the speed of the first ball before it hit the second one.