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Re: why pseudowork (NOT)

I agree with all said by John. Nothing strange in this inelastic
collision.

Note that applying the (pseudo) W-E Th to the two-mass system gives 0 = 0
cuz this theorem knows nothing about changes in internal energies of the
defined system.

Bob

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor

----- Original Message -----
From: John Mallinckrodt <ajmallinckro@CSUPOMONA.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Friday, October 29, 1999 12:55 PM
Subject: Re: why pseudowork (NOT)


On Fri, 29 Oct 1999, Richard Tarara wrote:

I have a problem with mechanism. Assuming momentum conservation then
the 1
kg block moves backwards with speed v.

There you go.

This also conserves the CM motion so we can deduce no external forces.

That's what momentum conservation is predicated on.

However, the brief collision of the objects should be viewed as
adiabatic so no thermal energy (or internal energy) could be
transferred
{or as Jim would prefer, one object could not have heated the other}
but
somehow all of the KE of the 2 kg block must now be internal energy
while there is no change in energy of the 1 kg block.

I'm confused by your analysis here. There's no reason to believe that
there was no energy transfered from one block to the other. It might be
that way; it might not. The problem statement doesn't give you enough
information to know one way or the other.

So to answer your questions using the (pseudo) work energy theorem, no
work was done on the 1 kg block and a negative mv^2 worth was done on
the 2 kg block

Exactly so. Other work-energy relationships will give different
results.

(but by what?). But I can't imagine how such a collision could
happen.

I still don't understand the difficulty. This is nothing more than a
very
ordinary inelastic collision.

John Mallinckrodt mailto:ajm@csupomona.edu
Cal Poly Pomona http://www.csupomona.edu/~ajm