# Thread: Special Relativity Question.

1. Hey,

This may be child's play to you fabulous bunch. Here is the question.

A 100m long railway station platform is equipped with automatic barriers at each end which
can instantly be simultaneously raised or lowered across the track at the touch of a switch. The
barriers are initially raised when a train of rest length 200m approaches the station at nearlight
speed.

a) How fast would the train need to be travelling for the station signalman to be able to
lower the barriers while the train was alongside the platform?
b) To the driver of the train, the barriers do not appear to be lowered simultaneously.
Which barrier appears to be lowered first and why?
c) How long does the driver wait before the other barrier is lowered?

This question is purely for revision purposes. For the first part I got v/c=sqrt(3/4) but I can not quite get my head around the second and third part.

Any help would be appreciated.

2.

3. This is just a version of the so-called pole-in-barn paradox

Moreover, it looks a lot like homework. You must figure it out yourself, with no outside help

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