ORIGINAL: Rogue
Do a search on resistance force. The faster an arrow is moving the more resistance it creates. Assuming you are shootingan arrow with decent mass I am willing to guess that the momentum is still holding at the farther distance while the resistance force is dropping.
Just a guess
Rogue
correct in a way. the faster the speed the more resistance UNTIL it maxes out speed which is a few ft past the end of the bow. which means it is loosing that resistance and becoming straighter by the ft. probably 6 or 7 yards max