Physics 171, Physics and Society Quiz 1 1pm Thurs Sept 14, 2017 Each question has one correct answer, or none (choose e on the clicker). 1.

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1 Quiz 1 1pm Thurs Sept 14, 2017 Each question has one correct answer, or none (choose e on the clicker). 1. Maria is riding her bicycle on a flat road at 10 mi/hr. Then she squeezes the brakes and comes to a halt. Once that process is complete, the kinetic energy of Maria and her bicycle has mostly been converted to (a) potential energy (b) thermal energy (c) electrical energy (d) nuclear energy 2. Which of the following is a major advantage of electric cars compared to gasoline cars? (a) batteries have a lower energy density than gasoline (b) electric motors are more efficient than gasoline engines (c) electric energy cannot easily be converted to kinetic energy (d) compared to buying a gallon of gasoline, it is much cheaper to buy the equivalent amount of electrical energy 3. When we say sugar contains about 4 Cal per gram, we mean (a) it takes that much energy to vaporize a gram of sugar (b) that is the energy released when a gram of sugar is dissolved in water (c) that is the amount of useful work a human body can do using the energy from a gram of sugar (d) that is the energy released when sugar is burned to CO 2 and H 2 O 4. How fast (to within 20%) would an object have to be traveling for its kinetic energy per gram to be the same as the chemical energy density of gasoline (10 Cal/g)? (a) 1 m s 1 (b) 100 km s 1 (c) 10 km s 1 (d) 1000 m s 1

2 Quiz 2 1pm Thurs Sept 21, Heat energy is a form of (a) kinetic energy (b) electrical energy (c) gravitational potential energy (d) nuclear energy 2. Absolute zero (zero degrees Kelvin) is the temperature at which (a) molecules move at roughly half the usual speed of sound (760 mi/hr) (b) molecules have fallen apart into atoms (c) molecules have no random movement (d) water freezes 3. To within 10%, what is the mass of a Nitrogen atom? (a) kg (b) kg (c) kg (d) kg 4. Gasoline consists of molecules that typically contain about 8 carbon atoms and 18 hydrogen atoms. Estimate to within a factor of 2 how many such molecules there are in a gallon of gasoline. (The density of gasoline is 0.7 kg/l.) (a) (b) (c) (d) 10 25

3 Quiz 3 1pm Thurs Sept 28th, If two objects are at the same temperature then (a) they each have the same total thermal energy (b) you can extract useful work from the heat flow between them (c) the molecules have the same average kinetic energy in each object (d) the molecules move at the same speed in each object 2. To make an internal combustion engine more efficient at converting heat to work, (a) the surrounding environment should be as warm as possible (b) the burning fuel should be as hot as possible (c) the burning fuel should be spread out over a large volume (d) it should use a fuel with very high energy density 3. Suppose you use a heat pump as your domestic water heating system. The water will be kept at 170 F, using heat pumped from underground rocks at 45 F. What is the maximum coefficient of performance of the heat pump? (a) 1.4 (b) 1.1 (c) 5.0 (d) Lake Michigan s average depth is about 100 m. If the temperature of the water increases from 15 C to 17.5 C, by how much (to 20% accuracy) will its depth change? (The linear expansion coefficient of water at at 15 C is C 1.) (a) 0.5 cm (b) 12 cm (c) 1.2 cm (d) 4 cm

4 Quiz 4 1pm Thurs Oct 5th, Radiation is (a) the emission of carbon dioxide when chemicals burn (b) the emission of posionous chemicals when atoms form bonds (c) the particles emitted when nuclei explode (d) the elements consumed when nuclei fuse 2. Which of the following are part of the electromagnetic spectrum? (a) neutrons (b) beta rays (c) alpha rays (d) gamma rays 3. The no-threshold linear hypothesis is (a) mainly used for predicting acute radiation sickness (b) widely used even though it may have large errors (c) reliable to within 30% for doses below 0.1 Sv (d) not applicable to doses of gamma radiation 4. The average American receives a background radiation dose of 0.01 msv (whole-body) per day. What is the number of resulting cancers per year in the U.S. (to within 20%) if the linear hypothesis is correct? (a) 2500 (b) 120 (c) 2 million (d) 40000

5 Quiz 5 1pm Thurs Oct 26th, Where does most of the gold in the earth s crust originally come from? (a) it was formed in hot lava when the Earth was young (b) it was created in neutron star mergers (c) it came from chemical reactions between light elements in the ocean (d) it was created in the big bang 2. When a Uranium nucleus undergoes neutron-induced fission, the products include (a) alpha rays (b) beta rays (c) microwaves (d) neutrons 3. In a lump of Uranium that is heavier than the critical mass, (a) each fission event causes more fission events (b) each fission event produces neutrons but no additional fission events (c) the neutrons escape from the Uranium and do not cause fission (d) the chain reaction is maintained by cosmic ray neutrons entering the Uranium 4. In February 2016, Sweden s central bank lowered its interest rate to a negative value of -0.5% per year. What is the half-life (to 10% accuracy) of money deposited in an account with this interest rate? (a) 14 years (b) 40 years (c) a negative number of years (d) 140 years

6 Quiz 6 1pm Thurs Nov 2nd, The role of Uranium in a nuclear reactor is (a) to heat deuterium and tritium so they fuse and liberate energy (b) to make neutrons that form an electric current (c) to provide heat to boil water (d) to provide fission fragments that ionize water 2. A conventional nuclear reactor cannot explode like a nuclear weapon because (a) the total amount of Uranium in a reactor is much smaller than in a weapon (b) the reactor does not contain fissile material (c) the accumulation of fission fragments suppresses further fission (d) when it gets very hot the chain reaction slows down 3. Nuclear waste produced in the U.S. is dangerously radioactive for over ten thousand years because (a) it contains 238 U which has a long half-life (b) there is still a significant amount of 235 U left in it (c) it contains Plutonium (d) it contains radioactive fission fragments 4. In a fusion reactor each fusion event produces about J. Roughly (to within a factor of 3) how much Helium is produced in a year by a fusion reactor whose output is 1 GW? (a) 20 kg (b) 200 kg (c) 2 tons (d) 20 tons

7 Quiz 7 1pm Thurs Nov 9th, The average temperature of the earth s surface is mainly determined by (a) the size of the earth (b) how fast the earth rotates on its axis (c) the ratio between amount of Oxygen and Nitrogen in the atmosphere (d) the balance between heating via sunlight and cooling via infrared radiation 2. A greenhouse gas means a gas that (a) is able to store a large amount of heat (b) encourages the formation of clouds (c) absorbs infrared light (d) emits visible or ultraviolet light 3. From ice cores, we can (a) obtain samples of the atmosphere from thousands of years ago (b) obtain pieces of the crust of the earth when it was first forming (c) learn the configuration of the continents a million years ago (d) learn about the evolution of mammals over the last million years 4. If earth s emissivity ε increases by 4%, then earth s temperature (a) decreases by 4% (b) increases by 4% (c) decreases by 1% (d) increases by 1%

8 Quiz 8 1pm Thurs Nov 16th, If the snow caps at the poles melt, the direct effect of this is (a) reduce earth s absorption fraction α e (b) increase earth s absorption fraction α e (c) decrease the solar constant F sun (d) increase the solar constant F sun 2. When natural gas (methane) is burned, it (a) emits no GHG (b) emits less GHG per kwh than coal (c) emits the same amount of GHG per kwh as coal (d) emits more GHG per kwh than coal 3. Carbon Capture and Storage (CCS) means (a) burning coal and burying the CO 2 that is produced (b) burning more expensive coal that contains only a small amount of carbon (c) using environmentally friendly methods to mine and store coal (d) switching from coal to natural gas 4. The U.S. uses 40 quads/year of electricity. To within 20% accuracy, how many 1 GW power stations are needed to meet that demand? (1 quad = J) (a) 15,000 (b) 5000 (c) 500 (d) 1500

9 Quiz 9 1pm Thurs Nov 30th, Which of the following is a form of solar thermal power generation: (a) Reflecting sunlight back into space to reduce global warming (b) Using sunlight to heat steam and drive turbines (c) Creating biofuels from sunlight via photosynthesis (d) Using sunlight to generate electricity via photoelectric cells 2. Which of the following is/are true? (a) Burning a biofuel produces very little CO 2 (b) Burning a biofuel does not add extra carbon to the carbon cycle (c) Burning a fossil fuel produces very little CO 2 (d) Burning a fossil fuel does not add extra carbon to the carbon cycle 3. A typical low-cost Silicon solar cell (a) provides energy at a cost of about 10 per kwh (b) is a heat engine using sunlight as a heat source (c) produces the same power in sunny and cloudy conditions (d) has an efficiency of about 15% 4. Suppose you eat 1 ounce (28 g) of fat, whose chemical composition is CH 2. When your body consumes the fat via respiration, how many grams of CO 2 will you breathe out (to 10% accuracy)? Atomic masses: Carbon-12, Hydrogen-1, Oxygen-16. (a) 28 g (b) 56 g (c) 85 g (d) 105 g