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Re: [Phys-l] FCI answer?



Not very. The drawing shows the puck moving from P to Q in the positive X
direction, and it shows the force acting perpendicularly in the +Y
direction. It then tells you that the force would produce speed Vk if the
puck were at rest. The questions then are about the direction, final speed,
and how the speed changes after the kick. The description is very exact and
is keyed to the drawing which has an extra visual clue by having arrows
showing the initial direction of the puck. I would say the extra arrows are
the only redundant information in the drawing. The written description does
not specify the direction of the kick so the drawing must be consulted.
Saying that V_k is in the direction of the kick is certainly not necessary
because everyone understands that a ball will respond in the direction you
push it when starting from rest. So I think there are probably only 2
redundant things in the description.

But it certainly should not lead one to think it is a case of a force which
is always perpendicular to the motion. This was the original supposed
ambiguity. These questions have been parsed by quite a few physicist
education researchers, many of whom are better than me, and as far as I know
they have not found any substantial ambiguities or errors.

John M. Clement
Houston, TX


Hmmmm....

I have not been following this thread.

Using the initial question statement provided by John C below, it
appears that
there is a force acting perpendicular to the line P-Q which passes
through position P.
However, we are asked to consider the effect of a force acting
perpendicular to
line P-Q, which passes through point Q, on a puck moving along the line
joining P-Q.
Somewhat over-specified??

Thought you'd want to know this
:-)

Brian W


John Clement wrote:
I for one, after reading the initial question statement do not think
there
is any ambiguity for this question. Compared to most questions I have
seen,
especially high stakes state exams, the question is posed quite
carefully.
If you look at only the part labeled #9, it is ambiguous, but not when
you
read the initial lead in paragraph.

Reading ability is not completely a separate item from physics.
Students
have to understand verbal descriptions of physics concepts as well as
graphical, pictorial, and finally algebraic. Here is the lead in
paragraph.
------------------------
Use the statement and figure below to answer the next four questions (8-
11).
The figure depicts a hockey puck sliding with constant speed v_o in a
straight line from point P to point Q on a frictionless horizontal
surface. Forces exerted by the air are negligible. You are looking down
on
the puck. When the puck reaches point Q, it receives a swift horizontal
kick
in the direction of the heavy print arrow. Had the puck been at rest at
point P, then the kick would have set the puck in horizontal motion with
a
speed v_k in the direction of the kick.
------------------------
There is a diagram showing the puck initially going straight to the
right,
and the kick perpendicular to the initial motion.

I do not believe there is any way to reword this to make it clearer. Of
course there are students, seniors no less in HS, who do not understand
the
word negligible, so if they ask I tell them it can be ignored. There
are
actually no "physics" terms such as force, velocity, or acceleration in
the
statement. Other than negligible it is in fairly plain language.

There is the fact that many students will not go back to the problem
statement, and look only at the question. This is actually a cognitive
deficit, and could probably be categorized by the Feuerstein taxonomy.
It
may come under the lack of need for accuracy and precision or possibly
also
excessive impulsivity. They may fail to look up V_k, mentioned in #9,
but
defined in the initial paragraph.

There is also the possibility that a student may have a very small
working
memory. But now we know this can be fixed or improved. There is a
program
of computer driven exercises that permanently expands the working
memory.
But it may be 20 years before schools actually routinely test for this
deficit, and attempt to fix it. A small working memory makes it
impossible
to keep all of the factors in mind when answering. This would generally
show up on the Lawson 2 variable reasoning questions.

All of these cognitive factors serve as a severe barrier to learning any
science or math, but there are programs that can help fix them, and some
of
these have been around since 1980, so why aren't they being used
routinely?
But of course it sometimes took a full generation for simple things like
sterilization to be routinely used in medicine.

John M. Clement
Houston, TX


It is ambiguity that started and sustained this thread. If there can be
multiple interpretations by professionals in the field, the question
then
becomes not whether the student uderstood the desired concept but
rather
whether the student read the questioners mind. What is being tested -
physics or reading ability?

Bob at PC

________________________________

From: phys-l-bounces@carnot.physics.buffalo.edu on behalf of John
Clement
Sent: Sun 2/15/2009 12:25 AM
To: 'Forum for Physics Educators'
Subject: Re: [Phys-l] FCI answer?



In the statement for problems 8-11 it clearly states that V_k is the
velocity the puck would have starting from rest, and it clearly shows
the
force in only one direction perpendicular to the initial motion. I
missed
the problem statement because in the copy in Mazur's book it is on the
previous page. Mea culpa, that was my mistake. The problem statement
is
exact and clear. Then only 1 trajectory is correct in problem 8, and
when
you pick that, the answer to problem 9 is also clear. There is no
ambiguity.






_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l



_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l