Problem Statement:

A jet engine on an airplane moving at 950 km/hr has an exit area of 0.50 m². If the gas exiting the engine has a speed of 1950 km/hr (relative to the jet engine) and a density of 0.50 kg/m³, how much thrust does the engine produce? If the airplane has two identical engines producing the same thrust, what is the total drag on the airplane? You may assume p_e = p0.

Solution:

First we need to know the mass flow rate of the fluid through the engine. This is found from

Then thrust is given by

This is the thrust for one engine. The total thrust produced by both engines is twice this, namely,

While the airplane is flying at steady speed (no acceleration), the thrust and drag balance (zero net force on the airplane). So, the drag on the airplane is