> free fall speed
They keep saying this. What they mean is "free fall acceleration".
It was a 110 story building with a ~70ft (6 or 7 floors) deep basement. 70ft/116floors = 0.6 feet (7.25inches) of space for each floor. A 3 inch concrete slab composed most of each floor's solid volume. Columns, ceiling materials, and office furniture don't add up to much. So there was enough volume in the cellar hole for most of the building to be crushed into.