Question

A rocket in deep space (zero gravity) accelerates by firing hot gas out of its thrusters. Does the rocket constitute a closed system? Explain.

a) Yes, because there is no external force acting on the rocket.
b) No, because the hot gas expelled from the thrusters constitutes an external force.
c) Yes, because the rocket is in deep space.
d) No, because the rocket is accelerating.

Answer 1

The rocket is not a closed system because it expels mass in the form of hot gas, separating it from the system.

Step-by-step explanation:

Does a rocket in deep space (zero gravity) accelerate by firing hot gas out of its thrusters constitute a closed system? The answer is no, the rocket does not constitute a closed system once it starts expelling gas. While in deep space there are no significant external forces acting on the system of the rocket plus the remaining fuel (such as gravity or atmospheric drag), the act of expelling the hot gas means that mass is leaving the system. Hence, the rocket and its fuel cannot be considered a closed system after the gas is expelled. By considering the rocket plus the expelled gas as a single system, we can apply conservation of momentum to describe the motion of the rocket, but once gas is expelled, that system no longer includes all components as they are now outside the rocket.