301 Test_1_Solution

301 Test_1_Solution - MAE 301: Engineering Thermodynamics I...

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1 MAE 301: Engineering Thermodynamics I Spring 2010 Test 1 (15% of final grade) February 16, 2010 Problem 1. (25 points) Air is contained in a vertical piston-cylinder assembly by a piston of mass 50 kg and having a face area of 0.01 m 2 . The mass of air is 5g, and initially the air occupies a volume of 5 liters. The atmosphere exerts a pressure of 100 kPa on the top of the piston. The volume of air slowly decreases to 2 liters as the specific internal energy of air decreases by 260 kJ/kg. Neglecting friction between the piston and the cylinder wall, determine the heat transfer to the air, in kJ. Solution: The pressure inside the cylinder kPa kPa A mg P P atm 149 0.01 9.8 50 100 + = + = From the First Law of Thermodynamics: () kJ m kPa kg kJ kg p u m W U Q 75 . 1 10 ) 5 2 ( 149 ) / 260 ( 005 . 0 3 3 1 2 = + = + Δ = + Δ = Problem 2. (25 points) A 90% efficient electric motor delivers power to a 75% efficient pump that
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301 Test_1_Solution - MAE 301: Engineering Thermodynamics I...

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