Post-Impact Speed of Colliding Billiard Balls

[rechitzy]

Homework Statement

Two billiard balls, one heading north at 15.0 m/s and a second heading south at 10.0 m/s, collide head-on. Take the collision to be perfectly elastic and choose the positive direction north.

What is the post-impact speed of the first ball
Answer: m/s

What is the post-impact speed of the second ball?
Answer: m/s

Homework Equations

The Attempt at a Solution

Don't even know where to start.

 

[Stonebridge]

You start by applying conservation of momentum and conservation of kinetic energy.

 

[rechitzy]

But don't i need the mass in order to do that?

 

[inutard]

They are identical billiard balls I assume, in mass and otherwise.