full-disclosure - **LosseChange::Debunk it??**

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Date: Wed May 17 17:36:37 2006
From: Valdis.Kletnieks at vt.edu (Valdis.Kletnieks@...edu)
Subject: **LosseChange::Debunk it??**

On Wed, 17 May 2006 16:49:39 BST, Pete Simpson said:
>                                                           In a
> pancake descent t = 110(2h/110a)1/2. According to my calculator that's
> just under 90s. So which calculation is incorrect?

That's an incorrect modeling of a pancake descent.  For starters, when
the structure fails, the top 20 or whatever floors all start descending.
They go one or two floors, and meet the first intact floor.  Now you
can treat this as an inelastic collision, and you now have 21 floors
descending at 20/21th of the speed and still accelerating. Then it hits
the 22nd floor from the top, and is slowed down even less... by the time
it gets 50 or 60 floors down, the top 20 floors have been accelerating for
a while, and each additional floor only costs 2% or so of the kinetic
energy to accelerate it.
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