Question

In a game of pool, a 0.4 kg cue ball is traveling at +0.80 m/s when it hits a slower striped ball moving at +0.38 m/s. After the collision, the striped ball moves off at +0.62 m/s.

What is the magnitude of the final velocity of the cue ball? Assume all pool balls have the same mass.

0.20 m/s
0.56 m/s
1.0 m/s

Answer 1

Use conservation of momentum (masses equal so m cancels):

v1i + v2i = v1f + v2f → v1f = v1i + v2i − v2f
= 0.80 + 0.38 − 0.62 = 0.56 m/s.

So the cue ball's final speed is 0.56 m/s.