Help with conservation of energy

1. Nov 8, 2007

engineer2010

1. The problem statement, all variables and given/known data
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.

2. Relevant 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

3. The attempt at a solution

2. Nov 8, 2007

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 ...

3. Nov 8, 2007

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.

4. Nov 8, 2007

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 ...