Everyone knows that films are make believe. Everyone knows whole chunks of movies would never stand up, let alone be achieved in so-called "real life". Right?
Apparently not. I have lost count of the number of times someone has watched a film with me and argued that something "could never happen" and thus suck the fun out of it, particularly action movies. (Note I'm saying nothing about narrative logic here: I'm talking about those moments in film that are incredible, but not so incredible within the world of the story we are watching).
For me it works like this: as long as your character does something that makes sense within the story, it doesn't have to actually be real or "work" in reality. If it did, we might as well stop making sci-fi films or any film where something out of the ordinary happens altogether. We'd only be able to make Ken Loach-style dramas. Now don't get me wrong, I actually love Ken Loach, Mike Leigh et al. But not all the time. Sometimes I want big explosions. And aliens. And werewolves. And tidal waves. And meteors. And people coming back from the dead with chainsaws. And everything else that opens Pandora's Box of Crazy Writing.
So if a hero jumps off a building then attached to a fire hose as Bruce Willis does in one of my all-time faves Die Hard, does it really matter if the science works?
Because it works in the story. John McClane is the type of guy who would do this. You or I would get barbequed, we'd be freaking so royally we'd never think of it - or if we did we'd make a mess of it and either still get barbequed or fall squillions of floors to our squishy deaths. That's assuming of course we'd be on top of the building at that exact moment anyhow: chances are I would be sitting downstairs with the rest of the hostages.
This isn't reality. Do what works for your story.
That said, the Open University does a rather impressive set of calculations for Bruce's jump here and whether he would survive. Pity Physics was never my thing and I haven't got a bloody clue what they're talking about. Enjoy!