Quick question about elastic collisions

[Hemichordate]

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In Examkrackers it says that for elastic collisions:

deltaK1 + deltaU1 = deltaK2 + deltaU2

It also gives

deltaK1 = deltaK2

1 = initial
2 = final

I know the first equation is the technical formula, but which one should be use on the MCAT? Should we consider potential energy for elastic collision problems?

 

[RogueUnicorn]

elastic collision is the conservation of kinetic energy

the equation on the top is a conservation of energy in general

 

[Hemichordate]

So the first equation is incorrect in this case?

 

[loveoforganic]

They're both right. The U terms just don't change for elastic collisions.