So a solid mass m drops distance h 3.7 m due to gravity g and hits a spring that compresses another d = 3.7 m (and then decompresses). What is the force F required for this and the energy E involved? Using the basic physics formulas previously quoted by me you should know that F = 2E/d.
As E happens to be (h+0.5d)mg and h = d, you find that F = 3mg in this imaginary case.
No need to calculate velocities and decelerations - just keep an eye on the energies involved and their origins, displacements, etc. because energy E is just force F times displacement.
What can we learn from this? Well, e.g. if something drops on a spring, the spring compresses and when the energy applied is absorbed by the spring (and force F is acting on the one end of the spring - and a force -F has developed at the other end at max compression d) the spring decompresses and pushes the solid mass m back up d and almost h (because some energy is lost as heat/internal friction in the spring). It's a bounce! The mass applied will fly up again due to a new force - the decompression force!
It is exactly like a child jumping in a bed as described in my article at
http://heiwaco.tripod.com/nist.htm that nobody has managed to debunk.
But you cannot really apply this basic physical phenomenon to WTC1 as mass m is not solid. Long before F is developed in the spring, a smaller force is applied on mass m that would be crunched into small pieces. That means that after contact the action after collapse initiation would soon be arrested.
Anybody believing (like NIST, Sunder, Bazant, Greening, Seffen etc.) that the WTC1 upper block is solid and impacting something springy is just a fool with no childhood and has never jumped in a bed.
In the solid NWO state jumping in beds is a security risk and anybody doing it is a potential terrorist.