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Re: [Phys-l] momentum and energy



Common Jack, now your just being cantankerous.

Writing in plain text (as is good etiquette here) restricts me from using
subscripts and superscripts, but it SHOULD be clear that the variables here
are Masses 1 and 2 (M1,M2), the initial velocities are V10 and V20, the
final velocities V1Fand V2F, and the Kinetic Energies KE10 (initial of
mass1), KE1F and KE2F the final kinetic energies. What's so hard about
that? All the 1s, 2s, 0s, and Fs would be subscripts in class, on the
test, etc. Sheesh...

Rick (who at least tries to run his messages through spell-checker. You
might try it Jack! ;-)


[Original Message]

I don't understand the notation. I insist the students define their
sumbols; that mightt help them obey your instructions.
Regards,
Jack

On Mon, 13 Nov 2006, Rick Tarara wrote:

If the students don't think well algebraically :-( then you might try
this.

Pull these equations out of a textbook (my students did for their last
test--despite instructions not to do that kind of thing):

Elastic collision with M2 initially at rest

V1F = (M1-M2)V10/(M1+M2)
V2F = 2M1V10/(M1+M2)

Now assume an elastic collision and calculate for different masses of M2
(the wall):

Taking M1 = 1 and V10 = 10 ---> KE0 = 50

M2 V1F V2F KE1F KE2F
1 0 10 0 50
10 -8.2 1.8 33.5 16.5
100 -9.8 0.2 48 2
1000 -9.98 .02 49.8 .2
10000 -9.998 .002 49.98 .02