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



Pls see comments after SNIPs:

--- Robert Cohen <Robert.Cohen@po-box.esu.edu> wrote:

Yesterday I asked my algebra-based physics I
students the following
question (in-class via student response system,
after a week of
discussion/homework/lecture on speed and
acceleration):

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.
B. The object's speed is not constant.
C. We are unable to determine whether the speed is
constant or not
without more information.

I asked this because I suspected students were
confusing speed and
acceleration (we haven't gotten into vectors yet).
I also wanted to see
if they would infer whether "speed is/is not
constant" referred to the
time period that extends from the initial time to
the final time.

I had twenty responses: A (2), B (11), C (7).

I then had the students discuss their choice and the
rationale for their
choice with at least one other person in the class.
Once they had
reached consensus with at least one other person,
they voted again.
This time the responses were B (12), C (8). SNIP

What was the rationale the students gave who chose
"C"? I wonder if the answers would be different if the
question were reframed with a familiar context. "A car
has an initial speed of 30 mph and a final speed of 60
mph". Same thoughts vis-a-vis the question posed
later. Is the use of a vague and/or context
confounding the results?

John Barrere
Fresno, CA