Elastic Vs. inelastic

[crazyasian]

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I've read several threads and from the various mcat prep books Im studying, I noticed that in every case where elastic and inelastic collisions are concerned the equation Pinitial=Pfinal then plugging in the mv for momentum is used for both elastic and inelastic. I remember from my physics class that we used the equation KE initial= Ke final then plugging in 1/2mv^2 for every elastic collision we Pintial-Pfinak for inelastic. Is there a case where i would use the Ke initial= ke final equation on the mcat, or am i safe to use the momentum equation? Thanks.

 

[Rabolisk]

Momentum is always conserved, but KE is only conserved during elastic collisions.

 

[eldoctor]

Momentum is always conserved, but KE is only conserved during elastic collisions.

Indeed, momentum is conserved whether the question is elastic or inelastic. You should be good using MV, and even if they ask for the kinetic energy, just use MV and plug into 1/2mv^2

 

[milla]

Yes. KE is only conserved during elastic collisions whereas momentum is conserved in both. The only time you would have to use 1/2mv^2 is to prove if the collision was completely elastic (i.e. KEinitial = KEfinal).

 

[crazyasian]

Ok That makes sense. Thank you.