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Re: COLLISION

Hi all-

At 09:37 11/26/99 -0500, David Abineri wrote:
When a moving railroad car collides with a stationary car of equal mass
elastically, the one car stops and the other begins moving with the same
velocity as the first.

If they now collide inelastically by coupling together, half of the
kinetic energy of the system is lost.

Now, my concern is, where has the kinetic energy 'gone'? Certainly air
was moved, sound was created and deformations took place but surely all
this happened in the elastic collision too.

Why should there be such a significant difference in the accounting of
energy between these two systems?

Any help would be appreciated.

First, simplify the situation by viewing it in the c.m frame.
Elastic: each car rebounds with the negative of its original momemtum. No loss in KE.
Inelastic: the cars couple and remain at rest. Total loss of KE.
Question: Where must the lost energy have gone? It must have gone into
the coupling mechanism - couplers on railroad cars are complicated hydraulic
devices which must dissipate huge amounts of energy.
Regards,
Jack

"I scored the next great triumph for science myself,
to wit, how the milk gets into the cow. Both of us
had marveled over that mystery a long time. We had
followed the cows around for years - that is, in the
daytime - but had never caught them drinking fluid of
that color."
Mark Twain, Extract from Eve's
Autobiography