# Predicting momentum change

1. Jun 8, 2014

### kidsasd987

If we know the initial momentum of particles a and b (mass a and b, initial velocity of a and b),
is it possible knowing the momentum after the collision without observing the velocity of two particles?
(well there is two variables therefore it seems impossible but we know that generally larger mass does not change its velocity much.)

We assume the collision is perfectly elastic.

Thanks.

2. Jun 8, 2014

### kidsasd987

hmm I think it is possible to 'approximate' the velocity after collision. if we assume some conditions such as contact time during the collision.

3. Jun 8, 2014

### mathman

In the center of mass coordinate system, the particle momenta add up to 0. The main question is whether there is any energy loss.

In the case of elastic collision, in the c.m. coordinates, each particle will have the same momentum before and after. In lab coordinates, it will depend on the angle of scattering.

Last edited: Jun 8, 2014