105 - exam 4 - Fall 2008 - solutions

105 - exam 4 - Fall 2008 - solutions - Fall 2008 Physics...

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Fall 2008 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. Fundamental c onstants: g = 9.80 m/s 2 G = 6.67 × 10 -11 N m 2 /kg 2 k B = 1.381 × 10 -23 J/K N A = 6.022 × 10 23 R = k B N A = 8.314 J/mol∙K = 0.08206 liter∙atm/mol∙K σ = 5.67 × 10 -8 W/m 2 ∙K 4 Conversion factors 1 inch = 2.54 cm 1 m 3 = 1000 L 1 atm = 1.013 × 10 5 Pa = 14.7 psi 1 cal = 4.186 J 32 5 9 + = C F T T 273.15 K C T T = + Note: all material constants that you should need for the exam are given here (not in the problems). Material properties Density of water: 1000 kg/m 3 Density of air: 1.29 kg/m 3 Young’s modulus of steel: 20 × 10 10 N/m 2 Linear expansion coefficient of brass: 19 × 10 -6 / ° C Specific heat of water: 4186 J/kg ⋅° C Specific heat of ice: 2090 J/kg ⋅° C Specific heat of steam: 2010 J/kg ⋅° C Specific heat of aluminum: 900 J/kg ⋅° C Latent heat of melting (water): 33 × 10 5 J/kg Latent heat of boiling (water): 2.26 × 10 6 J/kg Thermal conductivity of aluminum: 238 J/s m ⋅° C Average molar mass of air molecules: 29 g/mole 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 pressure sensor inside a tub of water is oriented to read the amount of pressure pushing down on it. How does the reading change when the sensor is turned upside-down (kept at the same height)? a. increases b. decreases c. stays the same 1. Pressure is exerted in all directions, like in the video we watched. Choice C. Problem 2. Which exerts more pressure on the ground, a 15000 pound elephant with four circular feet (each 12 inches in diameter), or a 150 pound clown standing on two stilts (each 2 inches in diameter)? a. elephant b. clown c. same 1
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2. P=F/A P elephant /P clown = (15000/(4 π 6 2 ))/(150/(2 π 1 2 )) = 1.38, so P elephant >P clown Choice A. Problem 3. In the “collapsing can demo”, why did the can collapse when the air was pumped out? a. Too much sucking force pulling on the inside b. Too much pressure from air on the outside 3. The force was applied by atmospheric pressure. Choice B. Problem 4. How deep does a scuba diver have to dive before the pressure is 2 atm? a.
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105 - exam 4 - Fall 2008 - solutions - Fall 2008 Physics...

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