2012 Thermodynamics Division C

Size: px

Start display at page:

Download "2012 Thermodynamics Division C"

Shannon Johns
5 years ago
Views:

1 Team: Team Number: Team Member Names: Instructions: Answer all questions on the test paper. If you need more room, you may attach extra paper. The test is worth a total of 50 points. Show all work where possible. Partial credit will be given where the work is shown, and legible. Answers without accompanying work will either be 100% correct or 0% Correct (little or no partial credit). If calculations are placed on a separate sheet, please provide an indication in the area provided on the test paper. For all test questions requiring a numerical answer, include units and the proper significant figures. You may not finish the test in the allotted time. Therefore, you are encouraged to complete the questions in any order that you choose. The test may be separated and split between the two team members as long as all the papers are placed back in the proper order. Before starting the test make sure that you have all of the problems numbered from 1 to 49.

2 Matching Directions: Put the correct letter next to the number. ½ points each 1. British thermal unit 2. Mechanical equivalent of heat 3. Specific heat 4. Sublimation 5. Latent heat 6. Evaporation 7. Conduction 8. Thermal conductivity 9. Convection 10. Radiation 11. Stefan s law 12. Internal energy 13. Thermometer 14. Thermal expansion 15. Absolute zero 16. First law of thermodynamics 17. Second law of thermodynamics 18. Third law of thermodynamics 19. Heat engine 20. Carnot Cycle A. Consists of two isotherms and two adiabats and is conveniently represented on a T-S diagram. B. Constant k C. Any device that converts heat energy to work D. A measure of temperature is obtained using a E. Lower limit of temperature F. It is impossible to reach a temperature of absolute zero. G. A process resulting from molecular interactions H J is equivalent to 1 kcal I. Heat transfers by mass transfer. J. Heat transfer needs no medium K. Heat, internal energy, and work are the quantities involved in a thermodynamic system. L. The energy becomes part of the total energy of molecules of an object or system. M. A solid undergoes a phase change and becomes a gas. N. A change in dimensions or volume of a substance that occurs when temperature changes O. The heat involved in a phase change. P. The rate at which an object radiates energy has been found to be proportional to the forth power of the absolute temperature (T4). Q. Certain processes do not take place, or have never been observed to take place. R. A Cooling Process S. The amount of energy required to raise the temperature of 1Kg of a substance by 1 C. T. A unit of heat that is commonly used in industry 1 Score:

3 Multiple Choice Identify the choice that best completes the statement or answers the question. Write the letter that best answers the question or completes the statement on the line provided. Following questions are ½ point each 21. Which of the following is a unit of temperature? a. Celsius degree c. kilogram b. joule d. Calorie 22. Heat is the transfer of thermal energy from one object to another because of a difference in a. specific heat. c. temperature. b. phase. d. waste heat. 23. As the temperature of an object rises, so does the a. kinetic energy of the object. c. thermal energy of the object. b. mass of the object. d. potential energy of the object. 24. Thermal energy depends on an object s a. mass. c. temperature. b. phase (sold, liquid, or gas). d. all of the above 25. How do you know that a sealed calorimeter is a closed system? a. because temperature is conserved b. because the masses of the sample and water are equal c. because thermal energy is not transferred to the environment d. because work is done on the test sample 26. Matter is needed to transfer thermal energy by a. conduction. c. radiation. b. convection. d. both a and b. 27. According to the first law of thermodynamics, the amount of work done by a heat engine equals the amount of a. work done on the engine. b. waste heat it produces. c. thermal energy added to the engine minus the waste heat. d. thermal energy added to the engine plus the waste heat. 2 Score:

4 28. Disorder in the universe increases because a. spontaneous changes produce more order in a system. b. work produces disorder in a system. c. work produces waste heat, which leaves a system. d. all of the above 29. One consequence of the third law of thermodynamics is that a. heat engines have efficiencies less than 100 percent. b. in some energy conversions, energy is not conserved. c. engines cannot discharge waste heat. d. the work a heat engine produces is less than the waste heat it produces. 30. Which of the following happens in a heat pump? a. The compressor increases the pressure and temperature of the refrigerant. b. The compressor blows cold refrigerant into the room. c. The compressor absorbs heat from the refrigerant. d. none of the above 31. Which of the following devices is based on the property of thermal expansion? a. balance c. convection oven b. calorimeter d. thermometer 32. The specific heat of copper is J/g C. Which equation would you use to calculate correctly the amount of heat needed to raise the temperature of 0.75 g of copper from 10 C to 25 C? a. Q = J/g C (25 C 10 C) c. Q = 0.75 g J/g C 15 C b. Q = 0.75 g J/g C 25 C d. Q = 0.75 g J/g C 10 C 33. In the formula Q = m c DT, which quantity is measured in units of J/g C? a. c c. Q b. m d. DT 34. What does a calorimeter directly measure? a. change in temperature c. specific heat b. kinetic energy d. Radiation 35. Energy from the sun reaches Earth mostly by a. conduction. c. radiation. b. convection. d. thermal expansion. 3 Score:

5 36. Which of the following materials conducts heat well? a. glass c. metal b. plastic d. Wood 37. To which of the following does the first law of thermodynamics apply? a. heating objects c. doing work on a system b. transferring thermal energy d. all of the above 38. The second law of thermodynamics states that thermal energy can flow from colder objects to hotter objects a. by convection. c. spontaneously. b. only if work is done on the system. d. when thermal expansion takes place. 39. Which of the following states that absolute zero cannot be reached? a. the first law of thermodynamics b. the second law of thermodynamics c. the third law of thermodynamics d. the second and third laws of thermodynamics 40. A fluid that vaporizes and condenses inside the tubing of a heat pump is called the a. compressor. c. refrigerant. b. fuel. d. condenser. 4 Score:

6 Problems Place your answers below the problems showing all your work and MAKE SURE YOU USE PROPER UNITS. All problems are worth 3 points each. 41. Two object have an initial temperature difference of 20C. In two minutes the temperature difference is 18C. Calculate the time for the temperature difference to be 10C. 42. A steel bridge is set in concrete pillars on opposite sides of a river. The bridge is 300m long, and the work is performed on a day when the temperature is 18C. What clearance is required for the bridge not to buckle at 45C? (α brass = 11 x 10-6 / C ) 43. How much heat is required to raise a 1.8kg copper tea kettle containing 2.0kg of water from 20C to 100C? The specific heat of copper is 0.092cal / g x C 44. A 150g cup of coffee (water) at 80C has added to it 20g of sugar (carbon) at 25C. What is the final temperature of the insulated mixture? (c c = 0.12 cal/g x C ) 45. Calculate the heat flow through a wooden door of are 2.0m 2 and thickness 5.0cm when the temperature difference is 20K. The k for wood is 0.10 W / m x K. 5 Score:

7 46. You eat 100 food calories worth of nuts. How high would you, at 65kg, have to climb to work off these 100 calories? 47. In a certain process 1.5 x 10 5 J of heat is added to an ideal gas to keep the pressure at 2.0 x 10 5 Pa while the volume expands from 6.3m 3 to 7.1m 3. What is the change in internal energy for the gas? 48. If an (gasoline) engine performs 10kW of work and is 28% efficient, what is the rate at which heat is taken in and expelled? (6 points) 49. An ideal monatomic gas at p a = 3.0 x 10 5 N/m 2, V a = m 3, and T = 27C expands adiabatically to p b = 2.0 x 10 5 N/m 2, V b = m 3 and then isothermally to V c = m 3. What is the final temperature, pressure, and work performed by the gas? Show these paths on a p-v diagram. 6 Score:

8 Matching Directions: Put the correct letter next to the number. ½ points each 2012 NATIONAL TOURNAMENT THERMODYNAMICS 1. British thermal unit 2. Mechanical equivalent of heat 3. Specific heat 4. Sublimation 5. Latent heat 6. Evaporation 7. Conduction 8. Thermal conductivity 9. Convection 10. Radiation 11. Stefan s law 12. Internal energy 13. Thermometer 14. Thermal expansion 15. Absolute zero 16. First law of thermodynamics 17. Second law of thermodynamics 18. Third law of thermodynamics 19. Heat engine 20. Carnot Cycle A. Consists of two isotherms and two adiabats and is conveniently represented on a T-S diagram. B. Constant k C. Any device that converts heat energy to work D. A measure of temperature is obtained using a E. The temperature at which a liquid becomes a solid F. Lower limit of temperature G. It is impossible to reach a temperature of absolute zero. H. A process resulting from molecular interactions I J is equivalent to 1 kcal J. Heat transfers by mass transfer. K. Heat transfer needs no medium L. Heat, internal energy, and work are the quantities involved in a thermodynamic system. M. The energy becomes part of the total energy of molecules of an object or system. N. A solid undergoes a phase change and becomes a gas. O. A change in dimensions or volume of a substance that occurs when temperature changes P. The heat involved in a phase change. Q. The rate at which an object radiates energy has been found to be proportional to the forth power of the absolute temperature (T4). R. Certain processes do not take place, or have never been observed to take place. S. A Cooling Process T. The amount of energy required to raise the temperature of 1Kg of a substance by 1 C. U. A unit of heat that is commonly used in industry

9 2012 NATIONAL TOURNAMENT THERMODYNAMICS KEY Matching Directions: Put the correct letter next to the number. ½ points each 1. T British thermal unit 2. H Mechanical equivalent of heat 3. S Specific heat 4. M Sublimation 5. O Latent heat 6. R Evaporation 7. G Conduction 8. B Thermal conductivity 9. I Convection 10. J_ Radiation 11. P_ Stefan s law 12. L_ Internal energy 13. _D Thermometer 14. _N Thermal expansion 15. E_ Absolute zero 16. K_ First law of thermodynamics 17. _Q Second law of thermodynamics 18. _F Third law of thermodynamics 19. C_ Heat engine 20. A_ Carnot Cycle A. Consists of two isotherms and two adiabats and is conveniently represented on a T-S diagram. B. Constant k C. Any device that converts heat energy to work D. A measure of temperature is obtained using a E. Lower limit of temperature F. It is impossible to reach a temperature of absolute zero. G. A process resulting from molecular interactions H J is equivalent to 1 kcal I. Heat transfers by mass transfer. J. Heat transfer needs no medium K. Heat, internal energy, and work are the quantities involved in a thermodynamic system. L. The energy becomes part of the total energy of molecules of an object or system. M. A solid undergoes a phase change and becomes a gas. N. A change in dimensions or volume of a substance that occurs when temperature changes O. The heat involved in a phase change. P. The rate at which an object radiates energy has been found to be proportional to the forth power of the absolute temperature (T4). Q. Certain processes do not take place, or have never been observed to take place. R. A Cooling Process S. The amount of energy required to raise the temperature of 1Kg of a substance by 1 C. T. A unit of heat that is commonly used in industry

18.13 Review & Summary

5/2/10 10:04 PM Print this page 18.13 Review & Summary Temperature; Thermometers Temperature is an SI base quantity related to our sense of hot and cold. It is measured with a thermometer, which contains