# Really Hard(for me) head on collision question

1. May 15, 2012

### ZxcvbnM2000

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

A snooker ball hits another one of the same mass head-on.If a quarter of the initial kinetic energy is dissipated in the collision ,what is the coefficient of restitution?

2. Relevant equations

Ei=Ef

3. The attempt at a solution

Energy statement:
ua+ub=(3/4)*(Va+Vb)

Momentum Conservation:

ua+ub=Va+Vb

Coefficient of restitution:

e=(Vb-Va)/(ua-ub)

But i cannot go further i have tried everything to get a result...could you please help me ?

The energy statement is wrong but for some reasons i can't put squares on each velocity.

Last edited: May 15, 2012
2. May 15, 2012

### Staff: Mentor

Since no specific conditions about initial speeds are given, why not consider the problem in the center of mass frame? Symmetry is your friend

3. May 15, 2012

### ZxcvbnM2000

Ah..can you be more specific ? I didn't quite get what you meant ! :p

4. May 15, 2012

### Staff: Mentor

What can you say about the speeds of the balls in their center of mass frame of reference? How does the expression for coefficient of restitution look in that frame? How about kinetic energy?