# Elastic and inelastic collision

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1. Jun 9, 2016

### mystreet123

1. The problem statement, all variables and given/known data
A low-energy particle collides elastically with a stationary particle of the same mass. The angle between the subsequent paths of both particles are 90 degrees.
But when a high-energy proton collides with a stationary proton, the angle between the two paths is not 90 degrees. Why is it so?

2. Relevant equations
½ mu2 = ½ mv2 + ½ ms2

3. The attempt at a solution
I answered that it's because the collision was not elastic so the above equation couldn't apply. But the answer is that because the proton is moving near speed of light so it's mass is greater than rest mass. So is this collision between the two protons still an elastic one? How to know whether a collision is an elastic or an inelastic one by its nature? I saw on some websites they say subatomic collisions are elastic but from another past paper it says the scattering between electrons and hydrogen nuclei is an inelastic collision...

2. Jun 9, 2016

### ehild

The collision is elastic if the colliding parties remain the same. If two protons collide, both of them remain the same protons. If an electron collides with a proton, you can get a neutron and a neutrino , for example; or you can get a hydrogen atom - these are inelastic collisions.

3. Jun 9, 2016

### mystreet123

Thank you so much!!