Re: SR examination question

[Jack Uretsky <jlu@HEP.ANL.GOV>]

But, John, the original question was:

> 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?

        So, Peter decays 1 minute after entering Jane's detector
(according to Peter), and Jane measures that time as \gamma times
1 minute.  The question does specify who makes each observation, no?
        The point is that "entering the detector" is an event
that "everybody" can use to start their stopwatches.  It is like,
in Einstein's little book, the event where the observers on the
train and on the platform are at the same point on the track.

                                Regards,
                                        Jack

On Fri, 18 May 2001, John Mallinckrodt wrote:

> On Thu, 17 May 2001, Jack Uretsky wrote:
>
> > On Thu, 17 May 2001, John Mallinckrodt wrote:
> > Hi all-
> >         But John's proper translation would give the same answer to
> > the question as my original translation.  So, John, where, in the new
> > context, is the ambiguity?
>
> Jack, The ambiguity is that my question (like the original one and
> unlike yours) does not specify who should determine how much time
> passes on my clock.  A nitpicker would point out that it could be
> *any* person.  I am simply pointing to the fact that there is no
> way of knowing whether that person rides on the muons or rides on
> my detector.
>
> Your question:
>
> > The muon has a lifetime of about 1 microsec (\mu_s).  A beam
> > of muons passes through my detector with a speed of 0.9c. What
> > lifetime do I measure for the muons?
>
> My question:
>
> > The muon has a lifetime of about 1 microsec (\mu_s).  A beam of
> > muons passes through my detector with a speed of 0.9c. During the
> > lifetime of a muon, how much time passes on my clock?
>
> John Mallinckrodt      mailto:ajm@csupomona.edu
> Cal Poly Pomona          http://www.csupomona.edu/~ajm

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