elastic collisions

[run-bandit]

elastic collisions relate to energy and not momentum right?

and you can always use the formula kx=mg when there is a hanging mass in equilibrium?

and we will not need to have a table of values of materials and young's modulus or places (like earth, mercury etc) and their gravitational field strengths on our cheat sheets?   

[superflya]

elastic collision= momentum + k.e conserved....

[Akirus]

so both criteria have to be met?

Correct.

[NE2000]

But to prove a collission is elastic in an exam you need not show that momentum is conserved. Energy will do.

[/0]

Yeah you can always use kx = mg is for a hanging mass, as long as it is in equilibrium and there are no other forces (like someone pulling the mass sideways). If it isn't a 'spring' question then use T = mg.
It's basically just an application of

All the data and equations you need to make calculations will be included in the formula sheet, so you won't need to include them on your cheat sheet. Your cheat sheet should include conceptual things to remember, and perhaps also sample explanations.