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Re: Help w/ Relativity Problem?

At 10:51 AM 4/2/96 EST, you wrote:

A spaceship has a length of 200m in its own reference
frame. It is traveling at 0.95c relative to Earth.
Suppose that the tail of the spaceship emits a flash
of light. (a)In the reference frame of the spaceship,
how long does the light take to reach the nose?
(b)In the reference frame of the Earth, how long does
this take? Calculate the time directly from the motions of
the spaceship and the flash of light, and explain
why you cannot obtain the answer by applying the
time-dilation factor to the result from Part (a).
(from Ohanian's Principles of Physics)

I would rather have the
understanding of the problem and work from there.

I also get 4.16 X 10 sec. Could someone please tell me what I'm missing
in this analysis:

From the earth's viewpoint, the nose is 200sqrt(1 - .95^2) or 62.45 meters
ahead of the tail when the flash is emitted. Also from earth's view, the
nose travels 0.95ct during the light's flight time. So the distance is
62.45 + 0.95ct

t = distance / c

t = (62.45 + .95ct)/c
t = 62.45/0.05c = 4.16 X 10 sec.

The distance the light travels, from earth viewpoint is 1248 meters.

An observer on the ship would say the light traveled 200 + .95cT
or 200 + .95c(6.67e-7)c = 390 m

1248sqrt(1 - .95*.95) = 390 (it seems consistant to me, making Ohanian's
answer wrong).
Stanley J. McCaslin Inet:
Assistant Professor, Computer Science Phone:402/872-2208
Peru State College, Peru, NE 68421 Home: 402/872-7595