Two equal-mass billiard balls collide elastically at right angles

[Ckoskie]

The question is:
- Two billiard balls of equal mass move at right angles and meet at the origin of an xy coordinate system. Ball A is moving upwards along the y-axis at 2.0 m/s, and ball B is moving to the right along the x-axis with speed 3.7m/s. After the collision, assume elastic, ball B is moving along the positive y axis. What is the final direction of ball A and what are their two speeds?

 

[Erik_at_DTU]

Kinetic energy maintained

The collision is elastic, and that means that the kinetic energy is maintained - just use that fact to find the answer