Question: Air flows from a large reservoir in which the pressure and temperature are 1 MPa and 30°C, respectively, through a convergent-divergent nozzle and into a constant area duct. The ratio of the nozzle exit area to its throat area is 3.0 and the length- diameter ratio of the duct is 15. Assuming that the flow in the nozzle is isentropic, that the flow in the duct is adiabatic, and that the average friction factor is 0.005, find the back-pressure for a normal shock to appear at the exit to the duct.