Midterm Solutions Please note, the order of the questions in your exam may be different from what is shown here. The questions, however, are the same.

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1 Physics 1110 Energy Fall 2009 Midterm Exam - November 5, Page 1 Name: Mail ID: Midterm Solutions Please note, the order of the questions in your exam may be different from what is shown here. The questions, however, are the same. PLEASE DO NOT LOOK AT THE CONTENTS OF THIS EXAM, OTHER THAN THIS COVER PAGE, UNTIL TOLD TO DO SO. This exam is closed book, but you may use one sheet of paper (both sides) with hand-written notes. Useful relationships: 1 calorie = 4.19 Joules g = 9.81 m/s 2 1 BTU = 1055 Joules 1 mile = km 1 gallon = liters Energy content of ethanol = 24.0 MJ/liter Directions On this exam booklet, please fill out your name, address, the date, and sign the pledge. On your bubble sheet, please fill in your name and the date in the spaces provided. Under Test please write Midterm, and under Class name/abbreviation please write Physics In the column on the right-hand side PLEASE BE CERTAIN to bubble in your UVa computing ID. Each multiple choice question has one and only one correct answer. On short answer questions (# 22 #27) please write a brief answer contained within the box that is provided. Multiple choice questions are worth one point. Short answer questions are worth two points. On my honor as a student of the University of Virginia I have neither given nor received aid on this exam. I have read all of the exam rules stated above, and have completed this exam honestly, according to those rules. Signed: Date:

2 Midterm Exam Noember 5, 2009 Page 2 1. Which of the following represent forms of pollution associated with coal? a. Sulfur b. Nitrogen oxides c. Carbon dioxide d. All of the above 2. A particular manufacturer quotes the heat output of a furnace as BTU s per hour. Convert the heat output to Watts (Joules/second). a. 9.7 Watts b Watts c. 1,026 Watts d. 10,257 Watts 3. When Feynman talks about the law of the lever what principle or idea is he trying to illustrate? a. The universal law of gravity. b. The conservation of energy. c. Mechanical advantage. d. That mathematics is the appropriate language of physics. 4. During one cycle, a heat engine draws 825 Joules from its hot reservoir, and does 300 Joules of useful work. How much energy is exhausted into its cold reservoir? a Joules. b. 525 Joules. c. It depends on the efficiency of the heat engine, so there is not enough information to answer. d. It depends on T H ad T C which are not given, so there is not enough information to answer. 5. As part of his description of the Principle of Irreversibility, Feynman describes trying to dry yourself off with several towels after getting drenched in a rain storm. In his analogy, what does dampness or ease of removing water represent? a. Temperature. b. Thermal energy. c. Work. d. Internal energy. 6. Which country has the largest reserves of coal? a. The United States b. India c. China d. Russia

3 Midterm exam November 5, 2009 Page 3 7. How does IGCC technology differ from standard combined-cycle technology? a. Petroleum can be used as the primary energy source. b. Natural gas can be used as the primary energy source. c. The two types of turbines are integrated into a single self-contained unit. d. Coal can be used as the primary energy source. 8. What has been the fractional increase in carbon dioxide since the beginning of the industrial revolution? a. Less than 1% b. Approximately 3.5% c. Approximately 35% d. Approximately 10% 9. If the United States were to exclusively use its current proven oil reserves (without replenishing those reserves) for its petroleum needs, how many years would it take to exhaust those reserves? a. About 3 years. b. About 10 years. c. About 30 years. d. About 50 years. 10. A heat engine has an efficiency of 22%. During each cycle, it produces 1200 Joules of useful work. How much thermal energy does the heat engine draw from its hot reservoir each cycle? a. 5,455 Joules. b. 26,400 Joules. c. 264 Joules. d. Not enough information to answer. 11. An interesting feature of IGCC technology is that a. it could help with the production of ethanol. b. it could help with the production of biodiesel. c. it would enable the more efficient use of natural gas. d. it can also be adapted to solar energy. 12. A person uses 2000 kilocalories in a day. What is the rate at which they use energy? a. About 23 Watts. b. About 97 Watts. c. About 2,328 Watts. d. About 83 Watts.

4 Midterm exam November 5, 2009 Page The cannonball engine (at right) runs in cycles in which the canister is moved from the cold water to hot water to lift a weight 0.1 meters, and the canister is subsequently moved back to the cold water to cause the piston to return to its starting position. The cold and hot water are kept at constant temperature, and each time a weight is lifted, 10 Joules of thermal energy is transferred into the canister. What is the change in the internal energy of the gas in the canister from the beginning of the first cycle to the beginning of the second cycle? 1.0 kg cold water hot water a. Approximately 11 Joules. b. Approximately 9 Joules. c. 10 Joules. d. There is no change. 14. A car with a mass of 1200 kg is traveling on the highway at a speed of 30 m s when the engine cuts out. The car coasts on level ground while being subjected to a constant frictional force of 2700N. How far does the car coast before coming to a full stop? (You may assume the driver never hits the brake.) a m. b. 133 m. c. 200 m. d. 400 m. 15. A car with a mass of 1500 kg is perched on the beginning of a hill. With negligible initial speed, it starts rolling down the hill, obtaining a kinetic energy of J upon reaching the bottom of the hill. How high is the hill? a m. b m c. 20 m d m 16. Why is it desirable to develop technology that would make it practical to produce ethanol using cellulose? a. It would increase the variety of crops that could be used to produce ethanol. b. It would make it possible to produce ethanol using land that was otherwise marginal for crop production. c. It makes it possible to use less energy input (fertilizer, diesel to run tractors, etc.) for each liter of ethanol produced. d. All of the above.

5 Midterm exam November 5, 2009 Page A car sold in Europe gets gas mileage of 13.6 km/liter. What is the gas mileage in miles per gallon? a. 32 mpg. b. 57 mpg. c mpg. d mpg. 18. Which of the following statements describing the Canadian tar sands is true? a. They represent proven reserves second in size only to those of Saudi Arabia. b. They represent a huge resource, but it takes more energy to recover them than one gets from the oil that is produced. c. They represent an important resource, but provide an insignificant (less than 1%) fraction of the oil used in the United States. d. All of the above. 19. If the United States were to use only domestic proven reserves of coal for its coal needs, how many years would it take to exhaust those reserves? a. About 20 years. b. About 50 years. c. About 100 years. d. About 200 years. 20. A Flex-Fuel car burns 8.5 liters of ethanol per hour. What is the rate at which thermal energy is being released by the fuel? a. 8.5 Watts. b kw. c kw. d Watts. 21. Which of the following can be produced using coal? a. Gas for lighting. b. Gas that can be used to produce electricity. c. Liquid fuel. d. All of the above

6 Midterm exam November 5, 2009 Page A 500MW power plant consumes coal containing BTU s of thermal energy every day. What is the efficiency of the power plant? Electrical energy produced by the power plant in one day: (500x10 6 J/s)(3600 sec/hr)(24 hrs/day)(1 day) = 4.32 x J Thermal energy in one day s worth of coal: (1.167x BTU s)(1055 J/BTU) = 1.23x J Efficiency = 4.32 x J 1.23x J = = 35.1% 23. Name the four primary energy sources that supply most of the energy consumed in the United States. Of these four, which supplies the most energy? Of these four, which supplies the least energy? Oil (the most) Coal Natural Gas Nuclear (the least) 24. What are some examples of energy infrastructure that have taken many decades to build? Railroads, coal-based power plants and uranium enrichment facilities are all examples. Other examples might include (but are not limited to) oil drilling and oil refining facilities, pipelines to carry oil, pipelines to carry natural gas and coal-mining facilities.

7 Midterm exam November, 2009 Page Isaac Asimov s short story The Last Question explored the implications of what physical principle or law? The 2nd law of thermodynamics, or equivalently, the fact that entropy always increases. 26. Why is the production of biodiesel from algae a particularly promising technology for the future? Algae-produced biodiesel is particularly promising because the land area required to produce it is much smaller than the land area required for any other biofuel. It is the only biofuel for which production could be scaled up to the amount of liquid fuel that is currently being consumed. The land area is small because it grows so quickly, doubling its biomass in 24 hours under the right conditions. 27. It has been suggested that natural gas could help serve as a bridge to an era in which we rely more on renewable energy sources. Give at least one compelling reason why shifting more toward the use of natural gas is a good idea. Because we have more natural gas (in terms of energy) than oil, and it is cleaner and would emit less CO 2 than coal.