So the initial velocity doesn't affect the force needed to stop a falling object...and the mass doesn't affect the force needed to stop a falling object...and the distance fallen doesn't affect the force needed to stop a falling object...
Tell me, what does affect the force needed to stop a falling object?
Good that you finally realize that a force F2 develops to stop a falling object when it contacts anything. According Bazant and NIST no such force develops. It is thus anything that applies this force on the falling object - not the other way around.
The first effect this force F2 has on the falling object is to decelerate it. According Bazant deceleration will not happen as F2 does not exist.
A second effect is that force F2 may provide high pressure/stresses in the structure of the falling body and cause deflections, deformations or failures. According Bazant failures in the falling body will not happen as the falling body has suddenly become rigid (indestructible). Why that is necessary is not clear as F2 does not exist.
Evidently the falling body applies a force -F2 on anything. As anything has velocity zero -F2 tries to speed up anything which is difficult as anything is fixed on the ground. So -F2 will produce local failures up in the top of anything.
As Bazant suggests that force F2 does not exist, then evidently the force -F2 cannot exist and you then wonder what is causing the local failures of anything that then continues into 'global collapse?
It seems that Bazant suggests that the falling object, after contact, first becomes rigid and then continues to accelerate and destroys anything (global collapse).
The children in my class cannot simply understand that. So I developed the PBT + impactor (a couple of extra pizza boxes) to show that F2 exists (Bazant and NIST objecting of course).
F2 is first of all a function of time. It only exists between first contact and arrest of falling object.
F2 is then a function of the structure of the falling object. If the falling object is, e.g. similar to a rubber ball, it bounces on anything. F2 will ensure that.
To avoid this to happen, Bazant assumes the falling object is rigid and that it cannot bounce, even if F2 doesn't exist in his NWO ivory tower.
F2 is also a function of the energy (J or Nm) transmitted to anything by the falling body at contact and until arrest.
F2 will ensure that this energy is consumed as deceleration, local deformations, failures, deflections (bouncing), friction (heat), etc. etc. between contact and arrest.
So far it is shown that F2 is not really concerned with the mass of the falling object, its velocity or drop height; those particulars are taken care of by just looking at the energy transmitted at contact.
Bazant carefully avoids mentioning this energy, because then he must explain what happens to it. Bazant instead invents that a shock wave develops in anything, etc, etc, and similar fairy tales.
If you read my papers (and posts) you will find that the upper block of WTC1 may provide about 1 GJ of energy at contact (assuming 'near free fall'). 1 GJ is not a lot of energy. 41 litres of diesel oil will provide it, if you want it, but then you need a very effective engine.
For the record, I do not believe in 'near free fall' because then all structure in the initiation zone between upper block and lower structure must have evaporated instantaneously, which is another 9/11 myth. But a I agree that some energy will be transmitted by upper block to lower structure at initiation, but it will be much less than 1 GJ. The result will be the same, just less local failures, etc, etc.
So you ask: Tell me, what
does affect the force needed to stop a falling object?
Answer is this force's capability to tranform energy of falling body into deceleration, local deformations, failures, deflections (bouncing), friction (heat), etc. etc. between contact and arrest.