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

[John Denker <jsd@av8n.com>]

On 09/11/2007 09:24 AM, Robert Cohen wrote:

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


Is this a question about _speed_ ... or is it a question about the
meaning of _constant_ and its relationship to _initial_ / _final_?

I ask because it would seem that with a modicum of test-taking
skills, it "should" be possible for students to answer the
following question correctly, even without the slightest idea
what "morgloid" means:

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


If "morgloid" is too abstract, substitute height or width or temperature
or cash_on_hand or some other quantity.

Is it possible to get information on how the students are doing on this
question (II)?

In particular, until students can reliably answer question (II) in a
non-speed context, it is premature to worry about whether they understand
speed.