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ME3251 Flow of Compressible Fluids Dr. T. J. Barber Spring 2013 Problem Set 1 Problem 1 Calculate the speed of sound at 288 K for the following gases: 1. Hydrogen, H2 2. Helium, He 3. Nitrogen, N2 Under what conditions will the speed of sound in H2 and He be equal? Problem 2 A supersonic aircraft flies horizontally at 1500 m altitude with a constant velocity of 750 m/s. The aircraft passes directly over a stationary ground observer. How much time elapses after it has passed over the observer before the latter hears the aircraft? Assume that the airplane creates a small disturbance that may be treated as a sound wave. Problem 3 A baseball, which has a mass of 145 grams and a diameter of 3.66 cm, when dropped from a very tall building reaches high speeds. If the building is tall enough the speed will be controlled by the drag, as the baseball will reach terminal speed. At this state W = FD where W (weight) = mg, g (acceleration of gravity) = 9.81 m/s2, FD (drag force) = CDρairAV2/2, CD (drag coefficient) = 0.5 and A (projected area of sphere) = πR2. Find the terminal speed of the baseball and determine the corresponding Mach number if the ambient air temperature is 23°C and the ambient air pressure is 101 kPa.