MEEN 315 PRINCIPLES OF THERMODYNAMICS SPRING 2017 Homework Cover page Student Last Name Student First Name UIN Section circle one HW Date Submitted 204 504 2 Grading Completion All problems attempted Quality Neatness clarity legible Accuracy Accuracy of selected problem s Cover page this page attached on the top and all pages stapled together Total 10 points Max Score 4 1 4 1 Your Score 10 This cover page should be completed and stapled to the top of your homework solution MEEN 315 PRINCIPLES OF THERMODYNAMICS SPRING 2017 Homework Assignment 2 Due Jan 31 2017 at the beginning of the class Problem 1 A box having a mass of 25 lbm is pulled horizontally across a rough surface by a cable such that the box experiences a constant acceleration of 8 ft s2 to the right At the same time friction exerts a force of 3 lbf to the left as shown in the diagram Assuming the box starts from rest determine a the amount of work performed by the action of the cable in lbf ft after the box has traveled 20 ft b the speed of the box when it has travelled 20 ft and c the change in kinetic energy of the box after it has traveled 20 ft lbf ft Hint you will need to use Newton s Second Law F ma and the relation Vfinal Vinitial at Acceleration 8 ft s2 Box 25 lbm Cable Friction Force 3 lbf Problem 2 A frictionless piston cylinder contains a substance initially having a pressure of 320 kPa and volume of 2 m3 The contents are heated causing the piston to rise Once the piston has risen to three times the initial height the piston encounters stops The heating process continues until the pressure inside the system is doubled Draw the entire process on a P V diagram pressure vs volume labeling the states 1 3 on the diagram and indicate the numerical values of pressure and volume corresponding to each state on the PV diagram Compute the boundary work W that occurred during the entire process from state 1 to state 3 in kJ be sure to indicate whether the work is in or out of the system Initial state 1 Piston hits stops 2 3h h P 320 kPa V 2 m3 Final state 3 MEEN 315 PRINCIPLES OF THERMODYNAMICS SPRING 2017 Problem 3 A newly constructed wind turbine has a blade diameter of 60 m It is installed in a field having steady wind speed of 8 m s 1 The density of air is 1 25 kg m 3 The efficiency of the wind turbine is estimated to be 32 Calculate the total electric power generated by this wind turbine If the selling price of electricity is 0 95 kWh how much revenue does this wind turbine generate in one year Problem 4 A piston cylinder assembly is filled with a gas which undergoes a process during which the pressure specific volume relation is pv1 2 constant The mass of the gas is 1 lb and the initial pressure p1 160 lbf in2 initial volume V1 1 ft3 At the end of the process the final pressure p2 390 lbf in2 Also during this process heat transfer from the gas to the surrounding is 2 1 Btu You may assume kinetic and potential energy effects are negligible Determine the change in specific internal energy of the gas in Btu lb Problem 5 A typical air conditioning unit installed in a house has a coefficient of performance of 3 5 This unit is capable of providing 3000 Btu h of cooling while in operation In a particular year the A C unit operated for 125 days at 8 hours per day If the occupants had to pay 11 cents per kW h for electricity determine the cost for cooling in dollars for that year
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