Pooh, Nikko presented some of his spreadsheet results here, regarding an idealised internal collapse of floor assemblies of WTC1:
– “The 10-storey section would take 0.88 s to fall the 3.8 meters before hitting the first floor below and in that time its velocity would increase from 0 m/s to 8.6 m/s. The collision with that floor (law of conservation of momentum) would reduce its velocity to 7.8m/s and the now 11-storey equivalent block would take 0.39 s to accelerate to 11.6m/s before again colliding with a floor, the impact of which would slow it down to 10.7 m/s. And so on and so on all the way to the ground through the remaining 98 floors, which it would hit after 11.7 seconds with a speed of 50 m/s.”
That’s well within the ~15 seconds of WTC1’s collapse.
My “back of a fag packet” momentum calculations are here. If you can face technical reading, the ROOSD collapse progression process is here. ROOSD is Rapid Open Office Space Destruction – cascade destruction of the floor assemblies, confined and thus channelled by the perimeter.