Q23. (a)
Write the equation giving the force required on a fluid control volume
to bring about a change in momentum and indicate three types of
forces which cause a change in momentum.
[4 marks]
(b)
A jet of water 30 mm in diameter and with speed 12 m/s strikes a plate
which is moving at 3 m/s in the opposite direction to the jet. The plate
is inclined at 25° to the jet.
(i) Assuming there is no friction between the water and the plate
surface, calculate the magnitude of the force exerted on the
plate by the jet.
[10 marks]
(ii) What direction does this force act in, relative to the plate?
[1 mark]
(c)
A jet-propelled aircraft is flying in still air at 180 m/s (Figure Q23). The
mass flow rate of the inlet air is $\dot{m}$ and the mass ratio of fuel to air is
3%. The exhaust gas from the engine exits at 540 m/s relative to the
engin. Derive an expression, in terms of $\dot{m}$, for the rate of change of
momentum of the fluid (in the horizontal direction) across the control
volume.
[5 marks]
fuel in
jet engine
air inlet
exhaust
gas
Figure Q23
control volume
