✔ 最佳答案
Yes, the centre of mass of the gas and the rocket system will move downward with an acceleration of 10 ms^-2.
It is because to consider the whole system, the upthrust force provided to the rocket by the gas is an internal force.
The only external force acting on the system is its own weight.
So, the centre of mass will accelerate downward with 10 ms^-2.