thrust
It will be OK as long as they don't apply all that thrust starting from zero velocity... the purpose of that much thrust is to overcome wind resistance at high speed, so if they start off at lower thrust and accelerate continuously at 3 G-forces or less, ramping up the thrust to counter wind drag at the same rate that the drag increases, the driver will probably survive the acceleration. I do hope they have done their aeronautical engineering well enough to be sure it will survive the shockwave produced when they break the sound barrier while flying at zero altitude...
