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105 - exam 4 - Fall 2007 - solutions

105 - exam 4 - Fall 2007 - solutions - Fall 2007 Physics...

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Fall 2007 RED Barcode Here Physics 105, sections 1 and 2 Exam 4 Please write your CID_____ Colton 2-3669 3 hour time limit. One 3 × 5 handwritten note card permitted (both sides). Calculators permitted. No books. Constants/some formulas: g = 9.80 m/s 2 G = 6.67 × 10 -11 N m 2 /kg 2 Mass of Sun = 1.991 × 10 30 kg Mass of Earth = 5.98 × 10 24 kg Radius of Earth = 6.38 × 10 6 m Radius of Earth’s orbit = 1.496 × 10 11 m I pt mass = mR 2 I sphere = (2/5) mR 2 I hoop = mR 2 I disk = (1/2) mR 2 I rod (center) = (1/12) mL 2 I rod (end) = (1/3) mL 2 Quadratic formula: 2 4 2 b b ac x a - ± - = Keep four significant digits throughout your calculations; do not round up to less than four. When data is given, assume it has at least four significant digits. For example “15 meters” means 15.00 meters. You are strongly encouraged to write your work on the exam pages and circle the correct answer. Of course also record your final answers on the bubble sheet . →Write your CID above upper right corner. Did you do this ________? You won’t get your exam back without writing your CID. Problem 1. A NASA training pool filled with water is 50 m long and 50 m wide, and 4 m deep. The absolute pressure at the bottom of the pool is __________ Pa. a. less than 109 kPa b. 109 – 119 c. 119 – 129 d. 129 – 139 e. More than 139 kPa gh P P ρ + = 0 = 1.01e5 + 1000*9.8*4 = 140200 Pa Problem 2. The pool is now half drained, and the top half is filled with a light oil (density 400 kg/m 3 ). The absolute pressure at the bottom of the pool is now: Oil and water: 1 0 1 1 2 1 2 2 2 0 1 2 P P gh P P gh P P gh gh ρ ρ ρ ρ = + = + = + + = 1.01e5 + 400*9.8*2 + 1000*9.8*2 = 128440 Pa 1
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Problem 3. When divers come up from the bottom of the pool, they experience a buoyancy force in the oil that is _________ the buoyancy force they felt in the water. The density of the fluid they displace is less, so buoyant force is less. Problem 4. Two pistons push on hydraulic fluid at rest. The diameter of the left piston is 5 cm. The diameter of the right piston is 1.3 cm. If the force on the left is 1000 N, the force on the right will be _________ N. Pressure is constant 1 2 1 2 2 2 2 2 1 2 1 1 1000 F F P A A A r F F A r = = = = 1000*1.3^2/5^2 = 67.60 N Problem 5. When an object is floating at rest, the buoyant force is _____ the object’s weight. a. greater than b. less than c. the same as Choice c. (from Newton’s 2 nd Law, object is in equilibrium)
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