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thermo2003quizsol

# thermo2003quizsol - Unified Engineering Quiz 1 Fall 2003...

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Unified Engineering Quiz 1 NAME WAITZ SOLUTIONS Fall 2003 Unified Quiz 1: Thermodynamics October 3, 2003 One 8 1/2 ” x 11” sheet (two sides) of notes Calculators allowed. N o books allowed. Put your name on each page of the exam. Read all questions carefully. Do all work for each problem on the pages provided. Show intermediate results. Explain your work --- don’t just write equations. Partial credit will be given (unless otherwise noted), but only when the intermediate results and explanations are clear. Please be neat. It will be easier to identify correct or partially correct responses when the response is neat. Show appropriate units with your final answers. Box your final answers. Exam Scoring #1 (40%) #2 (16%) #3 (24%) #4 (20%) Total 1

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Unified Engineering Quiz 1 NAME WAITZ SOLUTIONS Fall 2003 1) (40%, 8 parts * 5% each -- partial credit given) a) What does it mean for a process to be quasi-equilibrium? (LO# 4, 5) A process is quasi-equilibrium if the time rate of change of the process is slow relative to the time it takes for the system to reach thermodynamic equilibrium. b) Why is it necessary that a system be quasi-equilibrium (i.e. quasi-static) before applying many of the thermodynamics relations to that system? (LO# 4, 5) If the system is not in equilibrium, then different parts of the system exist at different states at the same time and it is not possible to define one “state” of the system. Since many of the thermodynamic relations relate to the state of the system, it is necessary that a state can be defined for the system before applying them. c) For a system composed of a small mass of gas passing through a rocket nozzle, describe the physical implications of an adiabatic, quasi-equilibrium (i.e. quasi- static) process. (LO# 4, 5) Such an assumption would imply that the mass of gas passes through the nozzle too fast for significant heat transfer to occur, but at a rate which is slow compared to the time it takes the small mass of gas to come to thermodynamic equilibrium. d) For a thermodynamic cycle involving an ideal gas, what is the relationship between work, shaft (or external) work and flow work when these quantities are calculated for the cycle as a whole? (LO# 1, 4) w = w + w f s w f = R( T) , only a function of the state of the system. Since the system returns to its initial state when completing one loop around the cycle, then w f =0 for a cycle and w=w s for a cycle.
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