Re: Controversial Exam Questions - Not Ohm's Law

[Michael Edmiston <edmiston@BLUFFTON.EDU>]

Leigh, how can you tell that B is the correct answer?

> A woman is standing on a flat section of ground. Her weight is 500 N.
> Newton's > third law states that there must be an equal and opposite force
to her
> weight, > which is
>
> A. the Earth exerting an upward force of 500 N on the woman.
>
> B. the woman exerting an upward force of 500 N on the Earth.
>
> C. the woman exerting a downward force of 500 N on the Earth.
>
> D. the Earth exerting a downward force of 500 N on the woman.
It seems to me that choices A and C are a third-law pair using the
definition that "weight is her contact force," whereas choices B and D are a
third-law pair using the definition that weight is "the force of gravity on
her."  If the question is referring to the A/C pair, then the force
described in the question text is C, and A is the answer.  If the question
is referring to the B/D pair then the force described in the question text
is D, and the answer is B.

What do you see in the question that tells you they are describing the B/D
pair?  Since it says she is standing on the ground, that might, in fact,
imply the A/C pair, because the B/D pair does not require that she be
standing... it requires no contact... it only requires an idea of what is up
and what is down in order to make sense of the spatial directions being
used.

If two different definitions of something are in current use, why do you say
an individual cannot have a bias toward one of them?

Michael D. Edmiston, Ph.D.              Phone/voice-mail:       419-358-3270
Professor of Chemistry & Physics        FAX:                    419-358-3323
Chairman, Science Department            E-Mail                  edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817