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Elastic collision rule



On an exam last Friday, one of my students solved a one-dimensional elastic
collision problem by setting the sum of initial and final velocities of one
particle equal to the sum of the initial and final velocities of the other
particle (and using this in addition to conservation of momentum). I have
not seen this approach before, and am wondering if it is a commonly taught
method. It is, of course, just a rearrangement of the more familiar (to me,
at least) rule that the relative rate of separation of the particles equals
their relative rate of approach. Do any of you teach collisions using this
student's method, or have you seen it presented in a textbook? (I'm
especially wondering if it might be a method that is common in high school
classes.)
______________________________________________________
Fred Lemmerhirt
flemmerhirt@mail.wcc.cc.il.us
http://chat.wcc.cc.il.us/~flemmerh/physics.html
Waubonsee Community College Sugar Grove, Illinois