What are the velocities of the balls after the collision?

[lozah]

Homework Statement

A 0.50 kg ball with a speed of 1.5 m/s in the positive direction has a head-on elastic collision with a stationary 0.80 kg ball. What are the velocities of the balls after the collision?

Homework Equations

I've used the Ek = (1/2)m(v^2) so far.

The Attempt at a Solution

I used the Ek formula above to find that the kinetic energy of the ball that was initially moving (0.50 kg at 1.5 m/s). It was 0.5625 J, and because it's an elastic collision, all of that Ek is conserved and the combined Ek of both moving balls post-collision should be 0.5625. I'm just unsure of how to find out which ball has which velocity now (the actual hard part of the question, lol). I've used substitution but I keep getting 0=0, lol! Can anyone help me out?

 

[BruceW]

what substitution have you used? remember, it's total momentum that's conserved.