Question

Two identical billiard balls are rolling toward each other at the same speed. What will be true after they collide head–on?

They will both stop rolling immediately after the collision.
One ball will stop rolling as the other bounces backward at a slower speed.
They will both bounce back at a faster speed after the collision.
They will both bounce back at the same speed they had before the collision.

Answer 1

After the head-on collision, both identical billiard balls will bounce back at the same speed they had before the collision. This is because of the conservation of momentum, which states that the total momentum of a closed system remains constant if no external forces act on it. In this case, the two billiard balls are a closed system, and their total momentum before the collision is equal and opposite to their total momentum after the collision. Therefore, they will both bounce back with the same speed they had before the collision.

Step-by-step explanation: