"In billiards, the cue ball has a mass of .17 kg and the other balls have masses of .16 kg. The cue ball, traveling at 2.9 m/s, strikes the 9-ball, which is at rest. After this collision, the cue ball continues at 0.5 m/s. What is the velocity of the 9-ball after the collision?"

Provide the magnitude of the velocity of the 9-ball after the collision (number only).