# Elastic vs inelastic collisions formulas

When doing practice problems from my textbook, I often get confused with both of them.
MOre specifically there are usually formulas which pertain to only one of those types of collisions.

Ex: $(v_1-v_2)_i = -(v_1-v_2)_f$

Does anyone know more of these types of formulas, or tricks to solve these equations?

Thanks.

mfb
Mentor
Does anyone know more of these types of formulas

or tricks to solve these equations?
- you can always use momentum conservation
- in elastic collisions, you can use energy conservation in addition
- in perfectly inelastic collisions, the objects stick together afterwards, so they have the same velocity
- in the center of mass system, all those collisions are easy to study

All equations are just a result of those ideas.

Elastic collisions: KE is conserved, momentum is conserved
Inelastic collisions: KE is not conserved, momentum is conserved.
This is a reasonable starting point

gmax137