Help with conservation of energy

[engineer2010]

Homework Statement

Two billiard balls move of equal mass move at right angles and meet at the origin of an xy coorindate system. Ball A is moving upward along the y-axis at 2.0m/s and ball B is moving to the right along the x-axis with a speed of 3.7m/s. After the collision, assumed elastic, ball B is moving along the positive y-axis . What is the final direction of Ball A and what is their speeds.

Homework Equations

Conservation of momentum :
MaVax+MbVbx=MaV'ax+MbV'bx

I know that the masses cancel as they are the same.
But that still leaves me with 2 unknowns in that equation. Do I have to use trig functions to fing the velociy of ball B and then use the momentum to find velocity of ball A?? but then how do i find the direction of ball A

The Attempt at a Solution

 

[catkin]

In an elastic collision linear momentum and energy are conserved. You have two independent lines (x and y) so that gives you three equations ...

 

[engineer2010]

O right sorry I forgot to write out the equation for the momentum along y. so in the x equation for example Vax= 0 and simiarly for the y equation? and is the third equation the kinetic energy one?? But I am sill confused as too how i find the direction of the A Ball.

 

[catkin]

Don't worry about finding the direction of the A ball; if you find its velocity in the x direction and its velocity in the y direction ...