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Re: [Phys-l] Sample relativity problem giving me fits...



For starters, let me suggest that there is a difference between
1) the spatial separation between the emission and absorption LOCATIONS as measured by O' and,
2) the spatial separation of the emission and absorption EVENTS, as measured by O'.

1) is calculated as the spatial separation between two SIMULTANEOUS (in O') events; this is what we refer to as "simple length contraction".
2) is calculated as the spatial separation between two NON-simultaneous events.

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
http://www.winbeam.com/~trebor/
trebor@winbeam.com
----- Original Message ----- From: "Jeff Loats" <loats_j@fortlewis.edu>
To: <Phys-l@carnot.physics.buffalo.edu>
Sent: Tuesday, January 16, 2007 1:01 AM
Subject: [Phys-l] Sample relativity problem giving me fits...


Hi all,

I am new to the forum, but hoping someone out there can help. I teach at
a small, relatively isolated, college and haven't had any luck working
this one with my colleagues.

Assume there is a light emitter at x = 0 and a light absorber at x =
150,000,000 m. Observer O' is moving along the x-axis at -0.8c and
watches some light get emitted and then absorbed. Here are the two
questions I had thought to ask...
a) What is the spatial separation between emitter and absorber according
to O'?
b) How long does the emit-absorb process take according to O'?

For part a) I believe we have simple length contraction, so we get 9x10^7 m.

For part b) I believe I can get this two ways. One I can find the travel
time for light towards the absorber which is moving away from the light.
If I do this I get 1.5 seconds. I also think I should be able to
time-dilate the time observed by O. The time O sees is 0.5 seconds,
which time dilates to 0.833 seconds, not 1.5 seconds.

I hope what I have said is clear. If anyone can point out what I am
doing wrong I would be very appreciative.

Jeff

--
Jeff Loats, Ph.D.
Assistant Professor of Physics
Fort Lewis College
650 Berndt Hall
970.247.7553
loats_j@fortlewis.edu
http://faculty.fortlewis.edu/loats_j/

_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
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