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On the other hand the value of the acceleration is positive assuming +
is to the right. When you ask if the answer is different for the value
of the acceleration if you assume a different direction of motion, many
students will say yes!!!!!
John M. Clement
Houston, TX
> -----Original Message-----
> From: Forum for Physics Educators [mailto:PHYS-L@lists.nau.edu]
> OnBehalf Of Kossom
> Sent: Wednesday, June 04, 2003 6:52 PM
> To: PHYS-L@lists.nau.edu
> Subject: Re: out-of-the-box thinking
/snip/
> I am fond of including essay questions on my tests.
>
> One of the questions I often ask during the acceleration section is
>
> Below is a series of lines made by a machine that marks
> the stripes on the street. If the machine always sprays the
> paint for the same length of time, is the machine speeding up,
> slowing down, maintaining a constant velocity or that
> can't be determined. Defend your answer.
>
> --- --- --- --- --- --- --- --- ---
>
> Most students say that the machine is speeding up, giving the usual
> reasons.
> This is a really easy question since we use tape timers in the lab.
>
> Over the years, though, a few students have noticed two problems with
> the question. Do you see them?
>
> Should I change the question, or isit good to let some students find
> them on their own? I give bonus points to students who find significant
> alternative answers or flaws. I hope that this encourages students to
> think
> outside the box on tests, but it can also cause students to go down
blind
> alleys on other tests.
>
>
> * * *
> Marc "Zeke" Kossover