Re: SR examination question

[Rick Tarara <rbtarara@SPRYNET.COM>]

I'm back to my statement "How many physicists....."

In my mind the original question is a simple 'moving clocks run slow'
question and aimed at introductory students where the instruction and the
text on SR goes little beyond:

1)  Moving clocks run slow
2)  Moving masses increase
3)  Moving length contract along the direction of motion

The only real problem with the original question, IMO, is that it is not
100% clear that Peter is moving and Jane is at rest although that (again to
me) is clearly the intent.  Once that is clearly established, then Peter's
watch reads less elapsed time than Jane's--'classic' twins-paradox stuff.
All the other fussing that has gone on in this thread seems to be ignoring
the context of the course for which it surely was intended.  Of course this
is not the first (or last) time a topic that started out as a discussion for
a H.S. or College intro course has turned into a free-for-all at the
theoretical dissertation level.  ;-)

Rick

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Richard W. Tarara
Associate Professor of Physics
Department of Chemistry & Physics
Saint Mary's College
Notre Dame, IN 46556
219-284-4664
rtarara@saintmarys.edu

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----- Original Message -----
From: "John Mallinckrodt" <ajmallinckro@CSUPOMONA.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Friday, May 18, 2001 4:35 PM
Subject: Re: SR examination question


> This has been a fascinating thread.  By my count, most people who
> have engaged in the correspondence, find the original question to
> be either unambiguous or, at least, clear in intent.  Those people
> are, I think, unanimous in interpreting the question as, "In the
> time that *Jane* says Peter's watch advances by one minute, how
> much time does *Jane* say her own watch advances."
>
> I am still curious about why that is.  Therefore, I'd be
> interested in anyone's answers to the following three question
> survey:
>
> Q1: How would you answer the revised question presented below?
>
> Q2: How does the revision differ from the original? (Be specific.)
>
> Q3: Do the differences *make* a difference?  Why or why not?
>
> The revised question:
>
>   "Peter and Jane are each wearing a wristwatch with a second hand
>   that takes one minute to make one complete revolution and Jane
>   is moving at a speed of 0.9c with respect to Peter. When the
>   second hand on Peter's watch has made one complete revolution,
>   how many revolutions will the second hand of Jane's watch have
>   made?"
>
> The original question:
>
>   "Peter and Jane are each wearing a wristwatch with a second hand
>   that takes one minute to make one complete revolution and Peter
>   is moving at a speed of 0.9c with respect to Jane. When Peter
>   observes the second hand on his watch to have made one complete
>   revolution, how many revolutions will Jane observe the second
>   hand of her watch to have made?"
>
> John Mallinckrodt      mailto:ajm@csupomona.edu
> Cal Poly Pomona          http://www.csupomona.edu/~ajm