# Billiard balls collision

1. Dec 12, 2007

### VanKwisH

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

Two Billiard balls of equal mass undergo a perfectly elastic head on collision
(Energy is conserved) . If the speed of one ball was initially at 2.0 m/s
and the other 3.0 m/s in the opposite direction, what will be their speeds after the
collision??

2. Relevant equations
m1v1 + m2v2 = m1v1' + m2v2'
1/2 m1v1^2 + 1/2 m2mv2^2 = 1/2m1v1 '^2 + 1/2m2v2 '^2

3. The attempt at a solution
so far i have simplified both formulas so that it's

v1' = v1 + v2 - v2'
v2' = v1^2 + v2^2 - v1 '^2

That's as far as a can go but i'm stuck what should my next step be......

The answer is v1 = 3 m/s & vs = 2 m/s if it helps anyone

2. Dec 12, 2007

### kplooksafterme

Well, you've done the bulk work of the problem already. You have two unknowns (v1 and v2 final) in two separate expressions. Use your algebraic skillz to solve (i usually substitute when there's only 2 unknowns, but you can eliminate too).