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).
I am curious as to how students in other classes might answer. If you
have a student response system and can ask this question, please let me
know what happens. For reference, my students are typically biology,
pre-pharmacy, physical therapy, environmental science majors and the
like. They are typically juniors and seniors and score about 25% on the
FCI prior to the course (like those at community colleges, I
understand). Pre-calc is a pre-req for the course and the course
includes a separate lab, not tied to the lecture.
By the way, after we discussed this question, I asked the following
question:
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/s^2
B. 3 m/s
C. Cannot be specified without more information.
The responses were: A (4), B (1), C (15)
Note: We have not yet discussed whether acceleration could be a slowing
down or changing directions. I wanted to make sure they understood the
difference between speed and acceleration before I introduced direction.
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Robert A. Cohen, Department of Physics, East Stroudsburg University
570.422.3428 rcohen@po-box.esu.edu http://www.esu.edu/~bbq