Unformatted text preview: Physics 2750 FS 2007 (white version) Exam 4 Last Name______________________________ First Name_____________________________ ID # ___________________ This is a closed book exam. I understand, pursuant to University Regulations on academic honesty, that I am not to use any notes or information other than what is in the official, non‐annotated formula sheet. Signature_______________________________________ For multiple choice questions, please make sure that you circle the letter for the answer which you believe to be correct and only that answer. If more than one answer is circled for the same problem, you will not receive credit for it. Don’t get hung up on questions. They should take only one or two minutes each. If you find yourself spending more than a few minutes on a multiple choice question you are probably looking at it the wrong way. You should skip it for now and come back to it later. For full credit show your work for solutions to questions that require calculations. Explain from where you start to solve the problem and show your math flowing from it for full credit. No shown work, no credit! Relax, read carefully, think – and then read everything again. During the exam, if you have questions please raise your hand and the TA or the instructor will come to you and provide help. 1. Which one of the following processes represents a decrease in entropy? a) the melting of ice b) the vaporization of liquid helium c) the sublimation of carbon dioxide d) the condensation of steam e) the evaporation of perfume 2. An adiabatic free expansion refers to the fact that a) no heat is transferred between a system and its surroundings. b) the pressure remains constant. c) the temperature remains constant. d) the volume remains constant. e) the process is reversible. 3. The most correct statement below regarding the First Law of Thermodynamics is that: a) A system can do work externally only if its internal energy decreases. b) The internal energy of a system that interacts with its environment must change. c) No matter what other interactions take place, the internal energy must change if a system undergoes a heat transfer. d) The only changes that can occur in the internal energy of a system are those produced by non‐ mechanical forces. e) The internal energy of a system cannot change if the heat transferred to the system is equal to the work done by the system. 4. Two identical rooms in a house are connected by an open doorway. The temperatures in the two rooms are maintained at different values. Which room contains more air? a) the room with higher temperature b) the room with lower temperature c) the room with higher pressure d) neither because both have the same pressure e) neither because both have the same volume 5. In a thermally insulated kitchen, an ordinary refrigerator is turned on and its door is left open. The temperature of the room: a) remains constant according to the 1st law of thermodynamics b) increases according to the 1st law of thermodynamics c) decreases according to the 1st law of thermodynamics d) remains constant according to the 2nd law of thermodynamics e) increases according to the 2nd law of thermodynamics 6. You chose to study at the University of Missouri Columbia because a) you heard about the wonderful courses in introductory physics b) of the exciting nightlife c) the academic programs all exciting and fun d) Chose? My parents MADE me come here because they have my best interest at heart! 7. The horizontal pipe, shown in the figure below, has a cross‐sectional area of 30.0 cm2 at the wider portions and 15.0 cm2 at the constriction. Water is flowing in the pipe, and the discharge from the pipe is 6.00 × 10‐3 m3/s. The density of water is ρ = 1000 kg/m3 and the density of mercury is ρ = 13600 kg/m3. Take g = 10 m/s2. 30 cm2 15 cm2 a) Find the flow speed in the wide portion. (5 points) b) Find the flow speed in the narrow portion. (5 points) c) What is the pressure difference between these portions? (5 points) d) What is the difference in height between the mercury columns in the U‐shaped tube? (5 points) 8. A well‐insulated bucket contains 200 g of ice at ‐5°C. How much tea at 70°C can you pour on the ice to get a cup of tea with a final temperature of 20°C? The latent heat of fusion for ice is 3.34 x 105 J/kg, the specific heat for ice is 2100 J/kg K and for tea is 4190 J/kg K (the same as for water). (25 points) Note: clearly specify (write in words) what each heat that you write represents. 9. A sample of 0.2 moles of a monoatomic ideal gas that initially occupies 5.0 L at a pressure of 2.4 atm is allowed to expand isothermally until its volume doubles. The gas is then heated at constant volume until its pressure is equal to its initial pressure. At last the gas is compressed at constant pressure to its original state. Take R = 8 J/molK, 1 L = 10‐3 m3, and 1 atm =105 N/m2. a) Draw the cycle on the PV diagram provided below and calculate P, V, and T for each state (fill out the values in the table provided). (15 points) P state 1 2 3 P V T V b) In which process is heat absorbed and in which is heat released? (3 points) c) Calculate the net work done in one cycle. Clearly show your calculations for each process. (8 points) d) Calculate the heat absorbed during one cycle. Take CV=3R/2. Clearly show your calculations for each process that absorbs heat. (6 points) h) Calculate the efficiency of an engine that works according to this cycle. (3 points) MC 30/ Q7 20/ Q8 25/ Q9 35/ Total 110/ ...
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- Spring '10
- First Law Of Thermodynamics, TA, Q7