A 2 kg billiard green ball is moving toward the 2 kg white billiard ball on a pool table. The green ball is moving with an initial speed of 4 m/s and the white ball is at rest. The two balls collide and move apart. The white ball moves away from the green ball with a speed of - 6 m/s. With what speed does the green ball move away?

10m/s

Explanation:

collisions results in objects sticking together or not sticking together after collision and so they do move with a common velocity or uncommon velocity respectively.

Parameters from the question:

Mass of green billiard balls, m1=2kg

Mass of white billiard balls, m2=2kg

Initial velocity for green billiard balls, u1=4m/s

Initial velocity for white billiard balls, u2 = 0m/s (since the body is at rest meaning it wasn't moving)

Final velocity of green billiard ball after collision is, v1 = unknown

Final velocity of white green billiard ball after collision is, V2 = - 6m/s.

Now from Newton's third law of motion that action and reaction must be equal and opposite; hence change in momentum before collision would be the same after collision since energy is conserved.

Hence,

m1U1 + m2U2 = m1V1 + m2V2

2*4 + 2*0 = 2*V1 + 2 * (-6)

8 = 2V1 - 12

8+12=2V1

20=2V1

10=V1

V1=10m/s