Rocket Thrust via Momentum Conservation

Steps:

• Thrust force F equals mass flow rate ṁ times exhaust velocity v_e: F = ṁ v_e.
• ṁ = 90 kg/s (mass ejected per second).
• v_e = 190 m/s (relative velocity).
• F = 90 × 190 = 17,100 N = 17 kN.

Why B is correct:

• Matches the rocket thrust formula F = ṁ v_e from Newton's third law, where ejected gas momentum imparts equal/opposite force on rocket.

Why the others are wrong:

• A: Underestimates by using incorrect velocity (e.g., ~23 m/s instead of 190 m/s).
• C: Overestimates by rounding velocity up to 200 m/s (90 × 200 = 18,000 N).
• D: Underestimates by using 180 m/s velocity (90 × 180 = 16,200 N).

Final answer: B