1. The problem statement, all variables and given/known data Standard pool balls have a mass of 0.17kg. Before a collision, ball A is at rest and ball B is traveling at 4.5 m/s [N]. After the collision, ball B is travelling at 1.6 m/s [N20E]. What is the velocity of ball A? 2. Relevant equations pinitial = pfinal m1v1 + m2v2 = m1v1 + m2v2 3. The attempt at a solution I believe that the initial momentum would be 0.17 * 4.5 m/s = 0.765kg m/s [N]. The momentum for B is 1.6 * 0.17 = 0.272 The initial momentum has to equal the final momentum, so: 0.765kg/m/s = 0.272 + A I drew a triangle for B's angle. For X component: 0.272 cos 20 deg = 0.255 For Y component: 0.272 sin 20 deg = 0.09 The X component will just be 0.255 [W] because the X component is 0. The Y component will have to be the difference between 0.765 and 0.09302, because you need the north to have the same momentum. The answer to that is 0.7168. Then I plug them all in and use Pythagorean theorem to find the momentum, which was 0.76 kg m/s. I divide that by the mass of 0.17kg and got a velocity of 4.2 m/s. But unfortunately, the answer is 3 m/s. How?