Re: [Phys-l] momentum and energy

["Richard Tarara" <rbtarara@sprynet.com>]

It's not a question of memorization for me.  I allow them a piece of paper
(one piece for the semester) that they can write equations on, but they are
admonished NOT to include solved problems or equations that pertain to very
special cases (of which the below are examples--not totally derived in
their text either).  However, since I did not specifically remind them of
that rule, I could only take a couple points off--but my collision problem
between an alpha and an Oxygen nucleus was no challenge for anyone with the
equations.  Actually I was trying to see if I could trip them up in that
the previous year's test had a collision between a proton and an alpha.  ;-)

Rick


> [Original Message]
>
>
> | 
> | 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)
> | 
>
>
> Amusingly enough, though not surprising, I have the same issues.
> Therefore on my last test about ten days ago one of the problems was:
>
> Derive the V1F equation above.  
>
> (I gave the equation to be derived, so those who had memorized the
> equation had no advantage.) 
>
> Those that merely memorized that equation . . .
>
> In a similar vein, I often ask range problems, where the "range formula"
> won't yield the correct answer.
>
> Its rather difficult to fight the rote memorization monster; but asking
> some questions where starting with basic principles yields the correct
> result and using some memorized expressions don't is one way.