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Re: Pendulum acceleration



That doesn't tell us anything about the level of understanding of the
students. In general, when a question gets such a low score,
you should
suspect there is something wrong with the question. In this
particular
case, the question is grotesquely ambiguous.


Whether it is grotesquely ambiguous or not is of course a matter of
aesthetic opinion (the grotesque part); the ambiguity part depends upon the
assumed context of the educational situation of the test takers.

A question can be ambiguous to an expert who is aware of certain issues that
may be relevant, but not ambiguous to a specific class that has been taught
specific items and contexts, and are not aware of the "certain issues" that
cause the problem to be ambiguous to the expert.

Naturally, you may have the occasional particularly knowledgable and gifted
student who is aware or figures out those issues. I have one currently in
my class. They usually are smart enough to figure out what the intended
question was in the context of the class and answer accordingly. Or they
are smart enough to clear up the ambiguity then and there (hard to do under
ACTSAT type conditions, admittedly). Or if they demonstrate to me they
understand the issues they were worried about and proceeded accordingly,
I'll give full credit.

In physics, the term "force" is well defined, but "net force"
is not. What
is included in the net, and what is not????

I wouldn't have quite phrased it that way. For others, try this phrasing:

Net force is well defined.

Fnet = Sum over forces

If its not well defined I'll have a tough time applying Newton's 2nd Law
when several forces are acting on an object.

What's not unique ("well defined") is the following: If all I know is the
LHS I can not uniquely decompose it into unique components on the RHS w/o
additional information.

E.g. a 1D example: Fnet = 10 for the LHS. The RHS could be 10, or it could
be (5+5) or (12 -2) or (3+2+5) etc.


========

Test-makers should not penalize students for analyzing the
system in ways
the test-makers failed to foresee.

=========================


This is of course a bit of a logical conundrum for the test maker
(particularly a computerized mass distributed multiple choice test). How
can they avoid problems that they fail to foresee?

Joel R