Two billiard balls of equal mass move at right angles and meet at the orgin of an xy coordinate system?

Question

Two billiard balls of equal mass move at right angles and meet at the orgin of an xy coordinate system. One is moving upward along the y axis at 2.0m/s, and the other is moving to the right along the x axis with a speed 3.7 m/s. After collision (assumed elastic), the second ball is moving along the positive y axis. What is the final direction of the first ball and what are thier two speeds?

Usually when working with billiard balls one is at rest during collisions, so the two balls being initially moving is confusing me.

Answer 1

An elastic collision means that kinetic energy is conserved, as is momentum.

However, in this case, your problem statement simplifies the situation, since the second ball replaces the first ball in its trajectory, which means that the first ball must have replaced the second ball in its trajectory.

Answer 2

Hi. One object hitting another with equal mass is about the same as hitting a brick wall, in this case at an angle. Try that approach. (The contact point of the balls would be at 45 degrees in this case.)