final_sol - (1 5 pts) The terminal speed of a parachute...

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( 1 – 5 pts) The terminal speed of a parachute whose diameter is 6.9m is found to be to be 6 m/s. The total mass of the chute and jumper is 120 kg. The density of the air is 1.23 kg/m 3 . What is the C D of the parachute? Sum of vertical forces = 0 so: C D ½ ρ U 2 A = mg C D ½ (1.23) 6 2 π (6.9) 2 /4 = 120 (9.8) C D = 1.42 ( 2 – 5 pts) Which of the following equations would be your best start to determine the average C D of an arrow whose mass is m and length is L and which decelerates from 250 m/s to 200 m/s over 150m. The density and viscosity of the air is also known. Note you do not necessarily need all this information to find the average drag coefficient, C D . (1) Σ Forces = 0 (2) C Davg = ½ ρ U 2 A (3) C Davg ½ ρ U 2 A = m (dU/dx) U (4) Re = ρ UL/ μ (5) C L = ½ ρ U 2 A ( 3 – 10 pts) Spherical hydrogen-filled balloon, D = 0.6 m is tied by a string to the ground. In stationary air the balloon exerts a vertical buoyant force of 1.3 N. When the air is moving at 3 m/s the balloon’s string makes an angle of 60 degrees with the ground. Please calculate the C D of the balloon. The density of the air is 1.23 kg/m 3 . T – tension in string; Tsin30 o = F D ; Tcos 30 o F B F D = C D A ½ ρ V 2 = F B tan 30 o C D = 1.3 (.58) / {[ π (0.6) 2 /4](1/2)( 1.23) 3 2 }= 0.48 ( 4 – 6pts) You know the length, wetted area and power to propel a ship at a known speed. You also know the density and viscosity of sea water. You know that the underwater surface of the ship is encrusted with barnacles. Think about how you would calculate the average roughness, L/ ε , of the barnacles (you only have equations , no graphs of C D vs Re L ). Write down the equations (I get 3) needed to estimate L/ ε given the given information above. You can’t give me a numerical answer, you can give me the equations and your plan to get L/ ε . Example: AB = L/
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This note was uploaded on 04/26/2010 for the course MAE 101B 101B taught by Professor Rohr during the Summer '09 term at UCSD.

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final_sol - (1 5 pts) The terminal speed of a parachute...

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