# Final velocities from head elastic head on collisions

## Homework Statement

Ball A with velocity +3.00 m/s collides with ball B with equal mass traveling at -2.00 m/s. What is the velocity of each ball after the collision.

Not sure.

## The Attempt at a Solution

I know that momentum is conserved because, but solving the conservation of momentum equation yields two unknowns. I also tried impulse-momentum theorem and conservation of kinetic energy, but I'm not sure how that will help. The answer is Ball has velocity -2.00 m/s and ball B has velocity +3.00 m/s. Is there a formula to actually solve for this because they don't give you either of the final velocities.

## Answers and Replies

How did you use the law of conservation of kinetic energy?

If you can put one of the velocities of the balls after the collision in term of the other , you can solve this problem.
And the law of conservation of kinetic energy would help you.

If you can put one of the velocities of the balls after the collision in term of the other , you can solve this problem.
And the law of conservation of kinetic energy would help you.
Well in my book they gave me a formula for relative velocity which is V2f-V1f = -(V2i-V1i). And I have the initial velocities and which will leave me with two unknowns still. Do I have to relate this somehow to conservation of kinetic energy and solve simultaneous equations?

Ahh I got it. Thank you!