# Momentum equation air jet

A jet engine is a reaction engine discharging a fast-moving jet that generates thrust by jet propulsion . This broad definition includes airbreathing jet engines ( turbojets , turbofans , ramjets , and pulse jets ) and non-airbreathing jet engines (such as rocket engines ). In general, jet engines are combustion engines.

In common parlance, the term * jet engine * loosely refers to an internal combustion airbreathing jet engine . These typically feature a rotating air compressor powered by a turbine , with the leftover power providing thrust via a propelling nozzle — this process is known as the Brayton thermodynamic cycle . Jet aircraft use such engines for long-distance travel. Early jet aircraft used turbojet engines which were relatively inefficient for subsonic flight. Modern subsonic jet aircraft usually use more complex high-bypass turbofan engines . These engines offer high speed and greater fuel efficiency than piston and propeller aeroengines over long distances.

The thrust of a typical jetliner engine went from 5,000 lbf (22,000 N) ( de Havilland Ghost turbojet ) in the 1950s to 115,000 lbf (510,000 N) ( General Electric GE90 turbofan) in the 1990s, and their reliability went from 40 in-flight shutdowns per 100,000 engine flight hours to less than one in the late 1990s. This, combined with greatly decreased fuel consumption, permitted routine transatlantic flight by twin-engined airliners by the turn of the century, where before a similar journey would have required multiple fuel stops. [1]

1. Free air is the air at

(a) atmospheric conditions at any specific location

(b) 20°C and 1 kg/cm2 and relative humidity of 36%

(c) 0°C and standard atmospheric conditions

(d) 15°C and 1 kg/cm2

(e) 25°C, 1 kg/cm2 and relative humidity of 50%.

Ans: a

2. Standard air is the air at

(a) atmospheric conditions at any specific location

(b) 20°C and 1 kg/cm2 and relative humidity 36%

(c) 0°C and standard atmospheric conditions

(d) 15°C and 1 kg/cm2

(e) 25°C, 1 kg/cm2 and RH of 60%.

Ans: b

3. 1 m of air at atmospheric condition weighs approximately

(a) 0.5 kg

(b) 1.0 kg

(c) 1.3 kg

(d) 2.2 kg

(e) 3.2 kg.

Ans: c

where F is the force exerted on a body of mass m and a is the acceleration. However, a more general form of Equation (2.55) is

which reduces to Equation (2.55) for a body of constant mass. In Equation (2.56), mV is the momentum of a body of mass m. Equation (2.56) represents the second fundamental principle upon which theoretical fluid dynamics is based.

We will apply this principle [in the form of Equation (2.56)] to the model of a finite control volume fixed in space as sketched in Figure 2.17. Our objective is to obtain expressions for both the left and right sides of Equation (2.56) in terms of the familiar flow-field variables p, p, V, etc. First, let us concentrate on the left side of Equation

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