Question

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. How does the velocity of the second pool ball compare to the original velocity of the first pool ball? A. The second pool ball's velocity will be less than the first pool ball's. B. The second pool ball's velocity will be the same as the first pool ball's. C. The second pool ball's velocity will be greater than the first pool ball's. D. The second pool ball's velocity will be exactly double the first pool ball's.

Answer 1

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)  

And that's literally 'velocity', not just speed.  The second ball must take off from the collision with the same speed AND in the same direction as the first ball.  

That's the only way that momentum can be conserved !