In a vacumn.

Right, and in a vacuum they keep accelerating until they hit something.

In air, water, whatever (besides a vacuum) there's going to be a limit due to drag (terminal velocity.

Sadly, that apple or feather rule is only good for letting us know that the Fg is the same on everything or when doing homework in high school and basic college physics where they get to ignore reality.

unless it's distilled water, and you know the exact temp...
and the precise mass and size of the object and the object is perfectly round...
it will vary to much

And yes, size does matter, the bigger it is, the more drag...And if the size of hte object get's close to the size of the container of water... you'll get a piston like pressure build up that slows it down even more...

yes, a lot of the common formulas assume a frictionless situation

The answer is: 7.678753 feet per second.

Now I suppose you'll ask; How good is that answer?

see disclaimer below.

downhill with a tailwind

my head hurts from reading all this.

yes, constant hard laughter can make your head hurt some

never had thjat problem

LOL! Thanks, I need that.