# Homework Help: I need the final velocity of two balls

1. Jul 27, 2008

### cuajin

m1 = 5, v1i = +10
m2 = 3, v2i = 0

+y
|_+x

How do I find v1f and v2f?

The balls crash into each other and after the crash I want to know the final velocity.

Last edited: Jul 27, 2008
2. Jul 27, 2008

### poopcaboose

Assuming the crash is a totally elastic collision all of the initial energy will be transfered into the kinetic energy of the first ball will be transfered to the second ball so you can use
E.Ki=m1v1i^2/2=m2V2f^2/2, so V2final will equal the square root of m1iV1i^2/m2 thats if it is a totally elastic collision if it is inelastic M.E. will equal the sum of both E.K

3. Jul 27, 2008

### cuajin

I was reading and looking at some of the animations on inelastic and elastic collision on Wikipedia and I have a very narrow idea of which is which.

1) Do you know a simple way of testing when a collision is elastic or inelastic?
2) If it is inelastic M.E. will equal the sum of both E.K, what does that mean? Sorry big noob here.

[EDIT] Just noticed something, is this right? velocity final 1 for inelastic collision is always equal to velocity final 2?
v1f = v2f?

Last edited: Jul 27, 2008