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Unformatted text preview: ramos (dar2447) – homework 36 – Turner – (58120) 1 This printout should have 11 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 10.0 points The small piston of a hydraulic lift has a crosssectional area of 7 . 2 cm 2 and the large piston has an area of 81 cm 2 , as in the figure below. F 7 . 2 cm 2 area 81 cm 2 What force F must be applied to the small piston to maintain the load of 85 kN at a constant elevation? Correct answer: 7555 . 56 N. Explanation: Let : A 1 = 7 . 2 cm 2 , A 2 = 81 cm 2 , and W = 85 kN . According to Pascal’s law, the pressure ex erted on A 1 must be equal to the one exerted on A 2 . The pressure P 1 = F A 1 must be equal to the pressure P 2 = W A 2 due to the load. F A 1 = W A 2 , so F = A 1 A 2 W = (7 . 2 cm 2 ) (81 cm 2 ) (85000 N) = 7555 . 56 N . 002 10.0 points The air pressure above the liquid in figure is . 69 atm . The depth of the air bubble in the liquid is 36 . 4 cm and the liquid’s density is 807 kg / m 3 . 36 . 4 cm air air Determine the air pressure in the bubble suspended in the liquid. The acceleration of gravity is 9 . 8 m / s 2 . Correct answer: 72775 . 7 Pa. Explanation: Let : ρ = 807 kg / m 3 , P = 0 . 69 atm , g = 9 . 8 m / s 2 , and h = 36 . 4 cm = 0 . 364 m . P = P + ρ g h = (0 . 69 atm) · 1 . 013 × 10 5 Pa atm + (807 kg / m 3 ) (9 . 8 m / s 2 ) (0 . 364 m) = 72775 . 7 Pa . 003 10.0 points A 42 kg woman balances on one heel of a pair of highheeled shoes. If the heel is circular with radius 0 . 496 cm, what pressure does she exert on the floor? The acceleration of gravity is 9 . 8 m / s 2 . Correct answer: 5 . 32552 × 10 6 N / m 2 . Explanation: Let : m = 42 kg , g = 9 . 8 m / s 2 , and r = 0 . 496 cm . ramos (dar2447) – homework 36 – Turner – (58120) 2 The pressure is equal to the force she exerts on the floor (which is equal to her weight) divided by the area of the heel: P = mg π r 2 = (42 kg) (9 . 8 m / s 2 ) π (0 . 496 cm) 2 · parenleftbigg 100 cm 1 m parenrightbigg 2 = 5 . 32552 × 10 6 N / m 2 ....
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This note was uploaded on 04/07/2011 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas.
 Spring '08
 Turner
 Physics, Work

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