Two billiard balls with the same mass m move in the direction of
one another. Ball one travels in the positive x-direction with a
speed of V1i, and ball two travels in the negative x-direction with
a speed of V2i. The two balls collide elastically, and both balls
change direction after collision. If the initial speeds of the
balls were v1i=2.0m/s and v2i =1.0m/s, what would be the final
speed and direction of ball two, v2f, in m/s? Thank...