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Re: [Phys-l] A simple (?) question about speed



I would be curious about students' written explanations for their answer
to the original question, where the final choice was NOT the correct
one. In that case, I believe that many students may be choosing "not
enough information" as a reflection of their lack of knowledge about how
to determine whether the speed is changing as opposed to claiming that
not enough information was provided to determine the correct answer.

Jeff Steinert
Physics and Chemistry Instructor
Arizona School for the Arts
1313 N. 2nd Street
Phoenix, AZ 85004
School: 602-257-1444
steinert@goasa.org
Home: 602-441-4810

From: "Robert Cohen" <Robert.Cohen@po-box.esu.edu>
Subject: Re: [Phys-l] A simple (?) question about speed
To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
Message-ID:
<47F49E5A3B3AA84F8DD701A3C515BF7B026920BD@tigger.admin.esu.edu>
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I also asked my colleague to ask the same question on her exam (as
"bonus") with the info about unknown changing speed included. Here are
her results:

At a certain moment, a car is moving toward the left at a speed of 30
m/s along a horizontal surface. You are given no information on whether
it is slowing down, speeding up or moving with a constant speed. What
is its acceleration?
A. 30 m/s2 (5)
B. 30 m/s (6)
C. Zero (5)
D. Cannot be specified without more information. (12)

My colleague also asked her students to provide a written rationale for
their answers. When I have some more time, I will go through and see if
I can find a pattern.

----------------------------------------------------------
Robert A. Cohen, Department of Physics, East Stroudsburg University
570.422.3428 rcohen@po-box.esu.edu http://www.esu.edu/~bbq