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Midterm Exam, Spring 2009

# Midterm Exam, Spring 2009 - Midterm Exam AEP 2640 Spring...

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Midterm Exam, AEP 2640, Spring 2009 Open book and notes; internet access is forbidden Time limit: papers will be collected at 4:00 1. Fluid Mechanics (36 pts) (A) ( 12 pts ) Calculate the horsepower needed to overcome drag on a sports car moving at a speed of 85 mph if the projected frontal area is 20 ft 2 and the drag coefficient at that speed is C D =0.38. Assume that the air density and kinematic viscosity are 0.074 lb/ft 3 and 1.56x10 -5 m 2 /s, respectively. [1 horsepower = 746 watts; 1 lb = 0.454 kg; 1 mile = 5280 ft; 1 inch = 2.54 cm] (B) ( 12 pts ) If we take a characteristic dimension “d” for the car to be given by the expression: πd 2 /4 = 16.5 ft 2 , calculate Re d . (C) ( 12 pts ) Would you expect the boundary layer over the car’s top surface to be laminar or turbulent? Why? 2. Error Analysis (36 pts) Ten independent measurements of the length and diameter of a circular cylinder of gold are given below: length (mm) diameter (mm) 20.025 4.875 19.975 4.900 19.975 4.850 20.000 4.875 19.950 4.850 19.950 4.900 19.925 4.925 19.950 4.950 20.000 4.950 20.050 4.975 (A) ( 12 pts ) What is your estimate of the standard deviation for each separate

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