Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

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



I teach a calculus-based physics course. Prior to seeing your
questions, the students had read two the relevant chapters (Chapter 6 &
7 of
<http://www.anselm.edu/internet/physics/cbphysics/downloadsI/cbPhysicsIa
17.pdf> )
done the relevant online quizzes (the Lec 06 quiz and the Lec 07 quiz at
<http://www.anselm.edu/internet/physics/cbphysics/downloadsI/OnLineQuizQ
uestionsIa1.pdf> )
and had one class session in which there was no lecture but in which
students responded to and discussed with each other and with me the
questions on pages 41-47 of
<http://www.anselm.edu/internet/physics/cbphysics/downloadsI/ClassQuesti
onsIa3.pdf>
Some of the students had done homework (due Friday) on that topic
(106-1,3 and 306-1 from
<http://www.anselm.edu/internet/physics/cbphysics/downloadsI/sacProblems
Ia12.pdf> )
See the student's responses below.


-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf
Of Robert Cohen
Sent: Tuesday, September 11, 2007 9:24 AM
To: Forum for Physics Educators
Subject: [Phys-l] A simple (?) question about speed

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.


The initial responses in my class were: A (0), B (19), C (2)
One objection to B was that the time interval, during which the reader
was being asked about the speed, was not specified and that the object's
speed may be constant during at least one relevant time interval. (A
student asked about this before all the responses were in and I said
that the question pertained to the entire time interval from when the
speed was 30 m/s to when the speed was 60 m/s but I don't know whether
all the students heard what I said or not.) The other objection was
that it seemed so obvious that the speed is not constant that it must be
a trick 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.


I modified this one slightly to stipulate that the motion was along a
straight path.

The initial responses in my class were: A (0), B (0), C (21)