Elastic vs inelastic collisions formulas

[oneplusone]

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]

Does anyone know more of these types of formulas

Sure, your textbook.

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.

 

[technician]

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

 

[gmax137]

Also, don't be confused by the word "elastic." In common usage, "elastic" is like a rubber band or a balloon, that is, something "stretchy." BUT, when we say "elastic collision" in physics, examples are hard steel ball bearings (like you see in a Newton's Cradle toy) or billiard balls. Collisions of soft stretchy things (like soft rubber balls) are likely to be "inelastic." Confusing? I thought so when I learned this stuff the first time.

 

[wasi-uz-zaman]

elastic collision

if masses of two objects is same than in elastic collision there velocities get interchanged and if masses are not equal than you can use the formula which u have given for elastic collision.