Originally Posted by
DaveReidUK
Your physics is fine, but it doesn't apply here - acceleration isn't a constant, for a start.
Yes, I'm aware of that: engines need to spin up, drag increases with velocity and when the aircraft rotates. The nice thing is that any nonlinearities in acceleration make the final velocity (ground speed!) be higher than 153.5 kt -- constant acceleration is the "most efficient" way to cover the distance and ends up with the lowest final speed of all possibilities (unless deceleration is involved).
Edit: this paragraph is nonsense.
So it's very much a back-of-the-envelope kind of thing (I doubt the take-off roll started an exact 2000m from the threshold, either); I don't claim to know what the actual speed was (hence my comment, "in theory").