posted by grey .
A 0.50 kg cue ball makes a glancing blow to a stationary 0.50 kg billiard ball. After the collision the cue ball deflects with a speed of 1.2 m/s at an angle of 30.0° from its original path. Calculate the original speed of the cue ball if the billiard ball ends up travelling at 1.6 m/s.
I think you can safely assume conservation of energy.
1/2 .5 V^2=1/2 .5 1.2^2 + 1/2 .5 1.6^2
solve for V