How Long Would It Take for a 747 to Stop, Like in 'Tenet'?

It's not uncommon for people to email me and ask me questions. If it's a question about a perpetual motion machine, I probably will just ignore it. But there was one email question that I didn't ignore. It went something like this—oh, it was from someone at Warner Bros. So clearly, this wasn't just a normal email.

Hello Rhett. We are working on a movie and we need your help. There is going to be a stunt in which we take a stripped-down 747 and get it up to 20 mph on a flat runway. Then we are going to stop it. So, the question: What is the minimum braking distance for this aircraft?

The email included some details like the estimated mass (200,000 lbs) and the fact that it has 8 of its 16 brakes installed. Oh yeah, I was interested in this challenging question. Game on. Little did I know that this was for a scene in the movie Tenet. It wasn't until I saw the trailer for the movie that I realized that the calculation I had performed was for this particular film.

OK, but how do you estimate the stopping distance for this 747? You can't just do an internet search for "stopping distance of a 747"—although, if you do you might find this page describing the physics of brakes heating up on 747 test stop (yes, I wrote it) . But this calculation shouldn't be too difficult, right? Isn't it something that you would cover in an introductory physics class? Well, that's a good place to start.

The key idea here is that of acceleration. Acceleration is defined as the rate of change of velocity. As an equation, it looks like this (in one dimension).

Illustration: Rhett Allain