Given that momentum is the product of speed and weight (Velocity x Weight) would rapid deceleration or acceleration in weighless space, of Space X's BFR have an impact on its passengers. I ask because if it is to travel at 27000km/h most of its journey would be spent accelerating and decelerating very much limited by earthlike g forces as airliners do, therfore minimizing on the reduction of travel time. Would most of the braking and accelerating have to take place in space at zero gravity?
The factor here is mass, not weight - weight is the force produced by mass and the effect of gravity.
The same kinds of forces are produced by acceleration. In "weightless space" (zero gravity) a spacecraft accelerating at 1g (9.81 m/s2) will impose the same force on its occupants as earth's gravity.
For a high speed spacecraft, a lot of the time will be spent accelerating and decelerating to keep the force on the occupants within tolerable limits.