M261 Soln Test-1

M261 Soln Test-1 - Solution to MAE 261 Test#1 February 9...

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Solution to MAE 261 Test #1 February 9, 2006 OPEN BOOK AND NOTES Note that units were not included in intermediate calculations below for brevity. They were required in student’s solutions. 1. a) What are the two major keys to flying faster and higher? b) When may we consider air to be incompressible? M<0.3 or V<100m/s c) What is the purpose of the dimples on the surface of golf balls? Reduce the drag 2. Consider a helium-filled balloon with a volume of 0.06000 m 3 . The balloon is at sea level on a standard day. The molecular weight of helium is 4 and the pressure and temperature of the helium inside the balloon is the same as that outside. a) Calculate the density of helium inside the balloon. R He = R / M He = (8314 J/(kg-mol K)) / (4 kg/kg-mol) = 2079 J/(kg K) ρ He = p/(R He T) = (1.013E5 N/m 2 )/(2079 J/(kg K)x 288.2 K) = 0.1691 kg/m 3 b) Calculate the buoyancy force on the balloon. B = ρ

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M261 Soln Test-1 - Solution to MAE 261 Test#1 February 9...

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