# Colliding particles with equal masses with given elasticity

1. Oct 28, 2007

### Superfluous

If the two particles with equal masses m collide with elasticity E = 0.650 , what are the final velocities of the particles? Assume that particle 1 has initial velocity v and particle 2 is initially at rest.

Give the velocity $$v_{1}$$ of particle 1 and the velocity $$v_{2}$$ of particle 2. Express the velocities in terms of v.

What I know...

$$mv_{1i}+mv_{2i}=mv$$

$$v_{2f}-v_{1f}=Ev}$$

I tried to use these two equations to solve for it, but it doesn't work out. My problem is that I know I'm supposed to use these equations to solve this, but I can't figure out exactly what to do with them. Solving the first equation for v and then substituting it into the second equation doesn't get me anywhere.

2. Oct 29, 2007

### Mindscrape

By elasticity do you mean coefficient of restitution? If so it is

$$\epsilon = \frac{|v_{2f} - v_{1f}|}{|v_{2i}-v_{1i}|}$$

you might have the wrong formula.

Also, another problem I see is that you are assuming an inelastic collision with your momentum equation. This is not necessarily true. Inelasticity works when your coefficient of restitution is zero, or approximately low.

3. Oct 29, 2007

### saket

I guess, the correct formula is, $$mv_{1f}+mv_{2f}=mv$$.
Now solve, you should get.