I just saw the Tv program Mythbusters (a few minutes of it).
They tried to bust the myth that the jet produced by the engines of a commercial airliner is able
to blow a car of the street and turn it over.
They took two jet engines of a much smaller size than those of 747's and propped them up on two trucks.
They then aimed the engines' jet at the car and turned them to full throttle. They couldn't blow the car over in their experiment but a few weeks later it happened in Argentina and it was captured on video.

What I don't understand is the buildup of the test.
Why do the jet engines on full throttle don't push the trucks forward?
Do the trucks just brake to prevent moving? Can the brakes hold the enormous power of a jet engine's thrust?
Or are there any blades/ disks in the engine itself that can turn the thrust on and off, thereby making it possible to have the engines run on full power but not giving any thrust?
I do imagine that when done right, you could strongly accelerate a truck with the help of a jet engine, no?
Has anybody seen this and/ or can explain?
Don Corleone, perhaps? I saw that you're a fan.