1. The problem statement, all variables and given/known data A white billiard ball with mass mw = 1.53 kg is moving directly to the right with a speed of v = 3.25 m/s and collides elastically with a black billiard ball with the same mass mb = 1.53 kg that is initially at rest. The two collide elastically and the white ball ends up moving at an angle above the horizontal of θw = 51° and the black ball ends up moving at an angle below the horizontal of θb = 39°. 1) What is the final speed of the white ball? 2. Relevant equations p=mv k=0.5mv2 Vcm = (M1V1 + M2V2)/ (M1+M2) 3. The attempt at a solution I don't really have any idea how to solve this. I started by first finding the velocity of the center of mass: Vcm = (M1V1 + M2V2)/ (M1+M2) Vcm = (1.53*3.25 + 1.53*0) / (1.53 + 1.53) Vcm = 4.9725/3.06 = 1.625 m/s And the initial momentum: P1i = M1V1i = 1.53*3.25 = 4.97 kg*m/s Since the collision is elastic, I know the final kinetic energy is equal to the initial, which means that K1f + K2f = K1i K1f + K2f = 0.5M1V1i2 = 0.5(1.53)(3.252) = 8.08 J Since momentum is conserved, I also know that the vertical momentum M1V1fy + M2V2fy = 0 And that the horizontal momentum of the two balls after the collision has to equal the initial momentum: M1V1fx + M2V2fx = 4.97 kg*m/s In the CoM frame, the 2 balls collide and then head off at the same speed, but for the life of me I can't figure out how to transform the speed in the CoM frame (1.625 m/s for each ball) back to the original frame without knowing what angle they are moving at after the collision in the CoM frame. And I don't know how to get the angles in the CoM frame from the angles in the original frame.