Chapter 15.9, Problem 142P

Air enters the intake scoops S at the rate of 50 m³/s. If the engine burns fuel at the rate of 0.4 kg/s and the gas (air and fuel) is exhausted relative to the plane with a speed of 450 m/s, determine the resultant drag force exerted on the plane by air resistance. Assume that air has a constant density of 1.22 kg/m³. Hint: Since mass both enters and exits the plane, Eqs.15-28 and 15-29 must be combined to yield

${\displaystyle \sum F_s=m\frac{dv}{dt}-v_{D/e}\frac{d{m}_e}{dt}+v_{D/i}\frac{d{m}_i}{dt}.}$