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From: hes@ecsvax.UUCP (Henry Schaffer)
Newsgroups: net.math
Subject: Re: Fly and train
Message-ID: <568@ecsvax.UUCP>
Date: Mon, 14-Oct-85 15:04:56 EDT
Article-I.D.: ecsvax.568
Posted: Mon Oct 14 15:04:56 1985
Date-Received: Wed, 16-Oct-85 04:19:33 EDT
References: <508@runx.OZ> <2092@brl-tgr.ARPA>
Organization: NC State Univ.
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<my article quoter is broken - I wish the same on many others>
The original article asked the question about a fly hitting a train
which was going at the same speed (velocity of fly = -v of train.)
It asked why when the fly's speed went to zero, doesn't the train's speed
go to zero, as well.

doug gwynn answered in terms of discontinuities.  Not contradicting
him, I think that the original question may have contained a different
problem.

The velocity constraint given in the original article is an initial
condition, not a constraint on continuing events.  Therefore, regardless
of what happens to the fly's speed, you don't know what the train's speed
is.  (Physics says that the train's speed after the collision depends on
the relative masses of the fly and train, ..., which weren't given.)
--henry schaffer