Originally Posted by james ozzie
...there is no fundamental reason why a reaction motor cannot travel faster than its own exhaust velocity, which is what the original poster asked.
For a jet engine, there
is a fundamental reason, and that is that the reaction mass flow
enters at the same speed as that of the 'reaction motor' (the aircraft) and
has to be expelled at a higher velocity to create thrust.
Furthermore, the notion that the reaction force is related to the airspeed implies that engine thrust diminishes as air speed increases - even during take off roll. This is clearly not the case.
I think what you've missed is that the mass flow
into the engine rapidly
increases with the airspeed at takeoff. More mass to accelerate, more thrust.
CJ