One of the promising applications of momentum principle is jet propulsion which has extensive applications in diversified fields. One of the classical example is rocket propulsion. Reaction of high velocity gases leaving the rocket nozzle produces thrust that propels the rocket in direction opposite to leaving jet of gases.
Linear momentum equation developed in the texts is limited to either fixed CVs or for those CVs which are translating with constant velocity, and is applied usually to steady flow problems. But a rocket will be accelerating and additionally losing mass as a result of continuous expulsion of gases. Hence in order to analyze the jet propulsion in rockets, one needs to consider the acceleration effect and unsteadiness.
Following CEP is intended to evaluate this phenomenon of jet propulsion in rockets and their resulting motion
In dynamics, by motion analysis using translating frame of reference, acceleration of a particle relative to fixed frame of reference XYZ, which is expressed in terms of motion observed relative to translating frame of reference xyz and motion of translating frame of reference xyz relative to fixed frame of reference XYZ, and is given as