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



The discussion about the two questions has been helpful. Here is an
update:

Just to remind you, two days ago I asked the following question (via
student response system, student responses in parentheses).

An object has an initial speed of 30 m/s and a final speed of 60 m/s.
Which of the following is correct?
A. The object's speed is constant (2)
B. The object's speed is not constant (11)
C. We are unable to determine whether the speed is constant without more
information (7)

Today I decided to change "speed" to "temperature" and asked the
following question. Keep in mind that most of the students had already
seen the previous question two days prior.

An object has an initial temperature of 30 C and a final temperature of
60 C. Which of the following is correct?
A. The object's temperature is constant (2)
B. The object's temperature is not constant (17)
C. We are unable to determine whether the temperature is constant
without more information (5)

Two of the people who chose A or C were not present in class two days
before.

I also had my colleague, who teaches a separate section of the same
course, to add these two questions to the exam she was giving today.
Half the students had one version and half had the other version. She
gave these as "bonus" questions and not all of the students got to it
(she suspects the weaker students did not get to the questions). Here
are her results:

An object has an initial speed of 30 m/s and a final speed of 60 m/s.
Which of the following is correct?
A. The object's speed is constant (0)
B. The object's speed is not constant (10)
C. We are unable to determine whether the speed is constant without more
information (3)

An object has an initial temperature of 30 C and a final temperature of
60 C. Which of the following is correct?
A. The object's temperature is constant (0)
B. The object's temperature is not constant (9)
C. We are unable to determine whether the temperature is constant
without more information (5)

I think we can conclude that use "temperature" instead of "speed" makes
little difference.

- -- - -

I also did an experiment with the other question I asked. Here are the
results from two days ago.

At a certain moment, an object is sliding toward the left at a speed of
3 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. 3 m/s2 (4)
B. 3 m/s (1)
C. Cannot be specified without more information. (15)

I changed "object" to "car" and asked the same question today, with the
added option of "zero" as an answer, and took out the portion about no
information about slowing down, speeding up, etc.

At a certain moment, a car is moving toward the left at a speed of 30
m/s along a horizontal surface. What is the car's acceleration?
A. 30 m/s2 (1)
B. 30 m/s (3)
C. Zero (3)
D. Cannot be specified without more information. (17)

Again, two of the people who chose A or B were not present in class two
days before.

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.

In the meantime, if anyone has the opportunity to ask these questions,
please let me know what happens.

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