The Car Tower at the end (Spoilers)
So, Ethan Hunt just drives the car to a (as Benji later puts it) "100 meter drop", which coincidentally is the distance the car would drop in the time it's in the air, falling.
Over that distance, the falling car would get to 100 mp/h. Crashing into a concrete wall (or floor in this case) at 40 mp/h is part of modern crash tests, so people geht out relatively unharmed.
At 60 mp/h, even with seatbelts and airbags, the driver hits bis head on the stearing Wheeler, resulting in head trauma.
At 100 mp/h, not even a secret agent can crawl out off that car, because an one would die...
Not that this is the most unbelievable scene in the movie, but it bothered me the most.
Still linke the movie, though.