100,000 pounds itself is not a lot weight for the interior of a skyscraper, and WTC 1 weighed roughly 10,000x that, if it were a lot parking garages would routinely collapse. Nor is it really all that much kinetic energy at 400 mph, under a thousand megajoules, parallel to the energy stored in a car's gas tank. Obviously once the collapse started the increasing amount of debris on each subsequent drop did the work, but it was really all about the energy released by the fuel, some 1000 times more energy than the kinetic energy of the plane, and from the plane a lot of that kinetic energy would have dissipated in the form of noise and moving derbis not just as raw heat inside the building. Realistically someone could have gotten the same effect by softly landing a helicopter with a similar amount of fuel on the building then spraying it inside and tossing a match, the crash itself might even have reduced the heat impact from all the broken windows serving as vents, or maybe not, ready source of fresh oxygen too.

Not trying to feed the conspiracist's here but realistically, all the broken glass and debris aside, a plane ramming into a skyscraper is roughly on par with throwing a hammer at a brick shed or hitting a TV with a baseball, you'll break the screen but the only way the frame's gonna collapse is if you knocked it off the shelf and it fell or if the baseball and circuitry caught on fire and melted it... which of course is what happened at WTC