ABSTRACT
This chapter illustrates how problems involving changes in mass can be handled. It provides an introduction to a topic which can form an interesting project for the undergraduate engineering student. The chapter considers the basic equations governing the motion of a rocket in flight, and attempts to predict the altitude gained by a model rocket with an engine of specified performance. A rocket engine produces gas molecules which are ejected with a high velocity; this causes a reaction which propels the rocket forward. To predict the motion of the rocket, it is necessary to obtain an equation which relates the forces acting on the rocket to its instantaneous acceleration. Forces are generally not applied to objects at a point but are distributed in their effect over a finite area. Under these circumstances, it is more useful to refer to a pressure; this is a force divided by the area over which the force is exerted.
