Question

What causes thrust of an engine?

(a) Change in momentum

(b) Difference in lift distribution

(c) Difference in drag distribution

(d) Mass flow entering the engine

The question was asked during an interview.

I need to ask this question from Jet Propulsion Engine Thrust in section Integral Form of Conservation Equation for Inviscid Flow of Aerodynamics

Answer 1

Right choice is (a) Change in momentum

Easiest explanation: The thrust is caused due to the difference in momentum of the air which leaves from the exhaust and the one that enters the engine. There is a presence of pressure difference between exhaust and the inlet which causes thrust.