exam1Soln

# exam1Soln - Phys 222 Spring 2006 Exam 1 Wed 15 Feb 8-9:30pm...

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Phys 222 Spring 2006 Exam 1, Wed 15 Feb, 8-9:30pm Closed Book, Calculators allowed Turn off all cell-phones, beepers, pagers Any call will result in the end of your exam Each question is worth one point, answer all questions Fill in your Last Name, Middle initial, First Name Your ID is the middle 9 digits on your ISU card. Please fill in your recitation section in special codes K to L For the H1 section please use section 18 At end of exam, please put exam writeup back in the folder, this allows you the chance to appeal the grading Best of luck, Craig Ogilvie

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1) In the morning you place two pieces of concrete (flat slabs of concrete) right next to each other, and between two fixed walls that cannot move. See top picture in the diagram. Each slab of concrete is 0.5m by 0.5m square and of minimal thickness. By the afternoon, the temperature has increased by 15 o C. The thermal coefficient for linear expansion of concrete is α =1.1 x 10 -5 . What height does the buckled junction reach by the afternoon (see the bottom half of the picture)? a. 0.7 cm b. 0.5 cm c. 0.9 cm d. 1.1 cm e. 0.3 cm Let h be the height at the center of the slabs, The expenaded length of slabs is L, original length is L 0 m h T L h T L h L T L h L T L L L h h L L 009 . 0 10 x 1.1 15 2 5 . 0 2 2 ) 2 1 ( ) 1 ( 5 - 0 2 0 2 2 0 2 0 2 2 0 2 2 0 2 0 2 2 2 2 0 2 = × × × = Δ = Δ = Δ + Δ + = = + = α
2) The figure below gives the temperature along the y-axis. The x-axis is the distance __through__ a wall that consists of three layers (A, B, C) of equal thickness. The air temperature on the left side of the wall is higher than the temperature on the right-side of the wall. Thermal conduction through the wall is constant (i.e. dQ/dt through the wall is a constant). Rank the three layers according to their thermal conductivities (k) a. kA = kB = kC b. kA> (kB = kC) c. kA > kB > kC d. kA < (kB=kC) e. kA < kB < kC insulator poor a i.e. R, small to ds corresopon T small a 1/k ~ R since check - Cross k. large a to correspond be must T small a hence surface), a at cumulate not does (energy layer each ough common thr is Δ Δ Δ = l T kA dt dQ 3) The figure below shows a plot of volume versus temperature for a process that takes an ideal gas from point A to point B. What happens to the pressure of the gas between A and B? a. stays the same b. increases c. decreases d. insufficient information to determine Since PV=nRT, the dashed line corresponds to constant P, (V ~ T, slope =nR/P). Since B is below this line, it must have a higher pressure.

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4) By what factor must the absolute temperature of a mono-atomic ideal gas be changed to double the rms speed of its molecules? a. 2 b. sqrt(2) c. 1/sqrt(2) d. 4 e. 1/sqrt(4) 4 of factor by T increases i.e. the doubles doubling constant / 2 3 2 1 2 2 T v T v v v kT v m rms rms rms = = => = 5) Two rooms, A and B, have equal volumes and are connected by an open door. Room A, which is air-conditioned, is 5 o C cooler than room B. Which room has more air in it?
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exam1Soln - Phys 222 Spring 2006 Exam 1 Wed 15 Feb 8-9:30pm...

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