So I have ball 'A' with mass 0.10 kg and velocity 1.4 m/s is travelling towards stationary ball 'C' with mass 0.10 kg. Ball 'C' is struck by ball 'A' and shoots off at an angle of 30 degrees to the x-axis, landing on the floor 1.20 meters below. I figured the time it takes the ball to hit the ground (0.5 seconds), and the velocity of ball 'C' after it is struck and travels at an angle of 30 degrees to the x-axis (0.36 m/s). Now I am asked to figure the y-axis value of momentum for ball 'A'. Momentum is conserved so p=mv => .1*1.4 => .14 (the total momentum before the collision). So I figure the y-axis value of the momentum for ball 'C' using p=mv and trig. and I come up with .018. So I have Pi=Pa+Pc (intial momentum equals the momentum of ball 'A' plus the momentum of ball 'C'). I can figure the momentum of ball 'A' after the collision, but I don't know at what angle the ball is travelling... So I'm stuck. How do I figure the y-axis value for the momentum of ball 'A'?