A pool ball with mass of 400g and a speed of 30 m/s hits another pool ball ( m = 400g) that's at rest.

A pool ball with mass of 400g and a speed of 30 m/s hits another pool ball ( m = 400g) that's at rest. If the first pool ball ends up going in the same direction with a speed of 10 m/s, what is the new speed of the second pool ball.