115Aex1win08verAsol

# 115Aex1win08verAsol - Name last first Student ID Number I A...

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Name ___________________________________ Student ID Number ____________ last first I. A pump (not shown) pulls water R Q h = 30 . 0 cm Direction of flow through a tube from point R past point Q. The tube radius varies from 5 . 00 cm at R to 20 . 0 cm at Q. Point R is 30 . 0 cm above point Q. The pressure at R is known to be P R = 1 . 20 × 10 5 Pa. Use g = 9 . 81 m/s 2 . The water has constant density 1000 kg/m 3 , and is known to have speed 18 . 0 cm/s at point Q. Ignore turbulence, viscosity, etc., and assume ideal flow conditions. 1. (5 pts) Which choice best represents the area (cross-section) of the tube at point R? 1 . 96 × 10 -3 m 2 1 . 96 × 10 -1 m 2 7 . 85 × 10 -3 m 2 7 . 85 × 10 -4 m 2 none of these A B C D E π r 2 2. (5 pts) Which choice best represents the water speed at point R? 0 . 72 m/s 1 . 02 m/s 1 . 44 m/s 2 . 04 m/s 2 . 88 m/s A B C D E A 1 v 1 = A 2 v 2 3. (5 pts) Suppose now that the flow rate is changed so that the fluid speeds at R and Q are v Q = 33 . 0 cm/s and v R = 5 . 28 m/s. If the pressure at R is unchanged, which choice best represents the pressure at point Q? 1 . 45 × 10 5 Pa 1 . 57 × 10 5 Pa 1 . 53 × 10 5 Pa 1 . 37 × 10 5 Pa 8 . 54 × 10 4 Pa A B C D E Bernoulli relates pressures at R and Q Physics 115A, Winter 2008, Version A Exam 1, page 1

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Name ___________________________________ Student ID Number ____________ last first II. A blacksmith forms a solid iron cube of mass 2 . 00 kg and width 6 . 40 cm (measured while in a mold at final temperature 700K). The air temperature in the room is 30 ° C when the iron block is removed from the mold. Some numerical values you may need: Stefan-Boltzmann constant σ = 5 . 67 × 10 -8 W/[m 2 K 4 ], emissivity of the iron block e = 0 . 82; specific heats : iron = 448 J/[kg K], air = 1004 J/[kg K], water = 4186 J/[kg K], ice = 2090 J/[kg K]; heat conductivities : air = 0 . 0234 W/[m K], water = 0 . 60 W/[m K], ice = 1 . 6 W/[m K], iron = 66 . 9 W/[m K]; thermal expansion coeffs : iron: α = 14 . 0 × 10 -6 K -1 , water: β = 0 . 21 × 10 -3 K -1 . Latent heat of fusion H 2 O = 33 . 5 × 10 4 [J/kg], latent heat of vaporization H 2 O = 22 . 6 × 10 5 [J/kg]. 4.
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115Aex1win08verAsol - Name last first Student ID Number I A...

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