A pool ball hits a second pool ball with equal mass. The first pool ball comes to a complete stop, while the second pool ball rolls away.
The second pool ball's velocity will be the same as the first pool ball's velocity was. (B) Â
And that's literally 'velocity', not just speed. Â The second ball must take off from the collision with the same speed AND in the same direction as the first ball. Â
That's the only way that momentum can be conserved !