Question

A rocket produces maximum thrust in vacuum because

• A. Mass flow rate increases in vacuum
• B. Exhaust velocity is higher in vacuum
• C. There is no atmospheric pressure opposing expansion
• D. Nozzle area increases automatically

Hint:

Rocket thrust equation: \[ \boxed{ F=\dot{m}V_e+\left(P_e-P_a\right)A_e. } \] As \[ P_a\downarrow, \] the pressure thrust increases. Maximum thrust is therefore obtained in vacuum.

Answer 1

The Correct Option is C

Step 1: Recall the rocket thrust equation. Rocket thrust is given by \[ \boxed{ F=\dot{m}V_e+\left(P_e-P_a\right)A_e, } \] where
• \(\dot{m}\) = propellant mass flow rate,
• \(V_e\) = exhaust velocity,
• \(P_e\) = exit pressure,
• \(P_a\) = ambient pressure,
• \(A_e\) = nozzle exit area.

Step 2: Consider operation in vacuum. In vacuum, \[ P_a=0. \] Therefore, \[ \boxed{ \left(P_e-P_a\right)A_e \] becomes maximum, resulting in higher thrust because there is no atmospheric pressure opposing the exhaust expansion. Hence, \[ \boxed{\text{There is no atmospheric pressure opposing expansion}.} \] Therefore, \[ \boxed{(C)} \] is the correct answer.