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# 17 - fryer(vdf96 Fluid Mechanics graves(6 This print-out...

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fryer (vdf96) – Fluid Mechanics – graves – (6) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points In a deep dive, a whale is appreciably com- pressed by the pressure of the surrounding water. What happens to the whale’s density? 1. Its density increases. correct 2. It cannot be determined. 3. Its density remains the same as before. 4. Its density decreases. Explanation: Since the mass is unchanged and the volume decreases, the density of the whale increases. 002 10.0points An engineer weighs a sample of mercury ( ρ = 13 . 6 × 10 3 kg / m 3 ) and finds that the weight of the sample is 7 . 0 N. What is the sample’s volume? The acceler- ation of gravity is 9 . 81 m / s 2 . Correct answer: 5 . 24675 × 10 - 5 m 3 . Explanation: Let : W = 7 . 0 N , ρ = 13 . 6 × 10 3 kg / m 3 , and g = 9 . 81 m / s 2 . m = W g so V = m ρ = W g ρ = 7 N (9 . 81 m / s 2 )(13 . 6 × 10 3 kg / m 3 ) = 5 . 24675 × 10 - 5 m 3 . 003 10.0points Air within the funnel of a large tornado may have a pressure of only 0 . 56 atm. What is the approximate outward force F on a 7 . 6 m × 22 m wall if a tornado suddenly envelopes the house? Atmospheric pressure is 1 . 013 × 10 5 Pa. Correct answer: 7 . 45244 × 10 6 N. Explanation: Let : P 0 = 1 atm = 1 . 013 × 10 5 Pa , P = 0 . 56 atm , a = 7 . 6 m , and b = 22 m . The inside pressure is 1 atm since the tor- nado envelopes the house suddenly. The force due to the air inside the house (pointing out- ward) is F outward = P 0 A = P 0 a b = (1 . 013 × 10 5 Pa) (7 . 6 m) (22 m) = 1 . 69374 × 10 7 N . The inward force due to the air outside the house is F inward = P A = P a b = (0 . 56 atm) (7 . 6 m) (22 m) × 1 . 013 × 10 5 Pa atm = 9 . 48492 × 10 6 N , so the net force on the house is F = F outward F inward = 1 . 69374 × 10 7 N 9 . 48492 × 10 6 N = 7 . 45244 × 10 6 N . 004(part1of2)10.0points In a car lift used in a service station, com- pressed air exerts a force on a small piston of circular cross-section having a radius of

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fryer (vdf96) – Fluid Mechanics – graves – (6) 2 4 . 26 cm. This pressure is transmitted by a liquid to a second piston of radius 16 . 6 cm. What force must the compressed air exert in order to lift a car weighing 13200 N? Correct answer: 869 . 315 N. Explanation: Let : r 1 = 4 . 26 cm , r 2 = 16 . 6 cm , and F 2 = 13200 N . Because the pressure exerted by the compressed air is transmitted undiminished throughout the fluid, F 1 A 1 = F 2 A 2 F 1 = parenleftbigg A 1 A 2 parenrightbigg F 2 = parenleftbigg π r 2 1 π r 2 2 parenrightbigg F 2 = (4 . 26 cm) 2 (16 . 6 cm) 2 (13200 N) = 869 . 315 N . 005(part2of2)10.0points What air pressure will produce this force? Correct answer: 1 . 52478 × 10 5 Pa. Explanation: P = F 1 A 1 = F 1 π r 2 1 = 869 . 315 N π (4 . 26 cm) 2 parenleftbigg 100 cm 1 m parenrightbigg 2 = 1 . 52478 × 10 5 Pa . 006 10.0points Why is the gas pressure inside an inflated balloon always greater than the air pressure outside? 1. Warmer air is inside the balloon. 2. Cooler air is inside the balloon.
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