Thank you for your replies;
I think I do not confuse the difference between TAS, GS! I just give you a quote of OAT-Notes:
Distance to accellerate/General Principles Take Off:
"From Netwon's laws of motion, the distance required for a body to reach a speed `V` from rest with a constant acceleration 'a' is : Vē/2a
This speed is True Ground Speed, wheras the lift off speed is an IAS."
Best
W.K.