phys (1201) - Space: rocket acceleration

practice question today, worth 4 marks, and after doing it, we had to mark other peoples responses to it.

the question asked to describe the acceleration of a 3-stage rocket anda bout the g-forces felt by the astronauts.

in the graph shown, g-forces gradually increased, dropped whenever an engine was shut off, and hit 0 between stages. that 0 would be when there's no thrust at all, in between stages, when a bit has been dropped off. free fall. because there's no reaction force acting on the rocket opposing gravity, so there's not even 1G.

now the acceleration increased because thrust (F) was constant, and mass (m) decreased as fuel was burned. to keep F=ma true, acceleration increased as mass decreased, and the formula for g-force is g-force = (g+a)/g so as a increased, the g-force did too.

we also did one more question, about conservation of momentum.

in a closed system like this, the rocket on the launch pad would have 0 momentum. but as it lifts off, it gains a momentum, and the fuel kicked out the bottom has momentum too, opposite and negative, so they add up to the initial momentum, 0, proving conservation