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[Phys-L] Re: Ambiguous Question



--- "Edmiston, Mike" <edmiston@BLUFFTON.EDU> wrote:

Would you please relieve me from reading your minds
by telling me
whether the prof should or should not give credit to
the students who
viewed the 3-m walk as 3 m relative to the dock.

I would side with the students. The question was
answered as it was asked.

Sometimes students add into a problem information that
is unreasonable. I have a different opinion then. For
example, assuming that this problem had been correctly
written, but a student had said that the boat wouldn't
have moved because the water was frozen, I would be a
bit miffed.

Sometimes students notice errors in my problems that
show additional physics insight. I try to give extra
credit in those situations. For example, given the
problem:

The picture below shows a striping machine
placing the stripes on a road. The machine
turns on for a short fixed time spraying a
line down. Is the machine that sprayed the
stripe speeding up, slowing down, or maintaining
the same speed? Defend your answer.

**** **** **** **** ****

I received a lot of interesting answers.

When I wrote the problem I assumed that the machine
was moving left to right, and since the distance it
was moving at each time interval was getting smaller,
the machine must be slowing
down. Several students saw the machine moving from
right to left and so it was speeding up. Since I had
my students defend their answers, I could tell which
way they saw it, and I was able to give them full
credit either way.

Some students saw that the question was ambiguous and
answered it both ways. Those students got bonus
points.

A couple of students also noted that, given the
description of how the machine works, the stripes
should be changing length. I gave those students extra
credit as well.




Marc "Zeke" Kossover
The Jewish Community High School of the Bay
San Francisco, CA 94121
<http://tochnit.jchsofthebay.org/~zkossover>



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