posted by James .
A 0.210 kg plastic ball moves with a velocity of 0.30 m/s. It collides with a second plastic ball of mass 0.109 kg, which is moving along the same line at a speed of 0.10 m/s. After the collision, both balls continue moving in the same, original direction, and the speed of the 0.109 kg ball is 0.26 m/s. What is the new velocity of the first ball?
Whatever conserves momentum.
Initial total momentum = Final total momentum
You have to do the calculation along one axis only in this case, since they remain traveling in the same direction.