physics exam 2007

Physics 140. Hour Exam II October 24, 2006 Name Discovery Room TA Section

Please do not open this exam book until you are told to do so. You will need 1. A #2 pencil 2. One scantron answer sheet 3. One exam question booklet 1. Use a #2 pencil; do not use a mechanical pencil or a pen. Fill in completely (until there is no white space visible) the circle for each intended input – both on the identification side of your answer sheet and on the side on which you mark your answers. If you decide to change an answer, erase vigorously; the scanner sometimes registers incompletely erased marks as intended answers; this can adversely affect your grade. Light marks or marks extending outside the circle may be read improperly by the scanner. 2. Print your last name in the YOUR LAST NAME boxes on your answer sheet and print the first letter of your first name in the FIRST NAME INI box. Mark (as described above) the corresponding circle below each of these letters. 3. Print your NetID in the NETWORK ID boxes, and then mark the corresponding circle below each of the letters or numerals. Note that there are different circles for the letter “I” and the numeral “1” and for the letter “O” and the numeral “0”. Do not mark the hyphen circle at the bottom of any of these columns. 4. This Exam Booklet is Version A. Mark the A circle in the TEST FORM box at the bottom of the front side of your answer sheet. DO THIS NOW! 5. Stop now and double-check that you have bubbled-in all the information requested in 2 through 4 above and that your marks meet the criteria in 1 above. Check that you do not have more than one circle marked in any of the columns. 6. Do not write in or mark any of the circles in the STUDENT NUMBER or SECTION boxes. 7. On the SECTION line, print your DISCOVERY ROOM. (You need not fill in the COURSE or INSTRUCTOR lines.) 8. Mark only one answer per question. 9. When told to do so: Check to make sure that the test booklet is complete. There are 10 numbered pages, including this cover sheet. 10. You have 60 minutes to complete the exam. 11. If you understand the statement below, please sign (DO NOT PRINT) your name on the STUDENT SIGNATURE line. If you do not understand, please ask the professor for clarification.

Academic Integrity—Giving assistance to or receiving assistance from another student or using unauthorized materials during a University Examination can be grounds for

disciplinary action, up to and including dismissal from the University

Page 1 of 10 pages (45 Problems)

Physics 140. Hour Exam I September 19, 2006

1. In Discovery room 5, you stood on a bathroom scale while riding in the elevator. Your classmate has a mass of 100 kg stands on the scale and weighs 1000N when the elevator is at rest. He remains standing on the scale when the elevator begins moving with constant acceleration, and you observe the scale to read 900 N. What is the acceleration of the elevator? A) 1 m/s2 downward B) 1 m/s2 upward C) 9 m/s2 downward D) 9 m/s2 upward 2. In Discovery room 5, you stood on a bathroom scale while riding in the elevator. Your classmate has a mass of 100 kg stands on the scale and weighs 1000N when the elevator is at rest. Imagine that the cable snaps and the elevator begins falling only under the influence of gravity. What would the scale read? A) 1000 N B) 980 N C) 0 N D) 2000 N 3. You have a spring that is 3 cm long that you want to use to shoot a ball across the floor. You compress the spring maximally, attach the ball to the end of the spring and place the spring against the wall. You let go, and the spring expands, shooting the ball. During which portion of the spring’s expansion did it do the most work on the ball? A) During the second centimeter. B) During the third centimeter. C) During the first centimeter. D) The work done is equal for all three segments of the spring’s expansion. 4. Cars are designed so that their bodies buckle (permanently deform) when they are in an accident. How does the buckling make the car safer by not allowing it to recoil (bounce) so much? A) The buckling stores energy. B) The buckling changes the collision energy into other forms. C) The buckling provides energy to the crashing objects. D) The buckling gives the car a high coefficient of restitution. 5. The coefficient of restitution between a ball and a surface is 0.50. If the ball bounces off of the surface and is observed to travel at 100 m/s after the collision. What was the speed of the ball before the collision? A) 100 m/s B) 150 m/s C) 200 m/s D) 50 m/s



6. Like a baseball bat, a tennis racket has a sweet spot at its center of percussion. If a tennis ball hits this center of percussion, the racket's handle does not accelerate. This is because A) an impact at the center of percussion exerts no torque about the racket's center of mass and doesn't cause the racket to undergo angular acceleration. B) the racket's center of mass accelerates backward while its handle rotates forward about its center of mass, and the two motions cancel one another at the handle. C) an impact at the center of percussion transfers no momentum to the racket and doesn't cause the racket to accelerate. D) the racket's velocity doesn't change when the ball hits its center of percussion. 7. You go through a loop in a roller coaster at constant speed. Where is your apparent weight a maximum? A) At the top B) At the bottom C) Halfway up, going down D) Halfway up, going up 8. The curves on bicycle racetracks are steeply banked, so that the inner edge of each curve is much lower than its outer edge. On a banked racetrack, what provides the centripetal force on the bicycle as it goes around the turn? A) the frictional force between the tires and the track. B) the weight of the bicycle. C) the support force of the track. D) (A) and (C). 9. When moving, a bicycle is in a state of dynamic equilibrium due to A) gyroscopic effects. B) air resistance. C) the shape of the fork. D) (A) and (C). 10. A three-wheeled vehicle is A) statically stable and dynamically unstable B) statically unstable and dynamically stable C) both statically and dynamically unstable D) both statically and dynamically stable



11. You are given a pair of socks for a birthday present. These are special socks that are made out of a very thin material, and they have small pieces of reflective metal woven into the fabric. How do these socks keep your feet warm in the snow? A) The metal carries heat from the surroundings by conduction to your feet. B) The metal reflects heat radiated from your feet back onto your skin. C) The metal keeps heat from being carried away by convection. D) The metal gets wet, and the evaporation warms your feet. 12. Soil heats up much faster than water when the two are exposed to sunlight. Use that fact and your understanding of heat transfer to predict which way the wind will blow near the surface of the earth as the sun sets near the seashore. A) The surface wind will blow from the land toward the water. B) The surface wind will blow alternately back and forth along the shore, parallel to the boundary between land and water. It will reverse directions every few minutes. C) The surface wind will blow steadily in one direction along the shore, parallel to the boundary between land and water. D) The surface wind will blow from the water toward the land. 13. You add a little hot tea to ice water at 0 °C; the mixture will remain at 0 °C so long as some ice remains. Where does the tea’s extra thermal energy go? A) It goes into the ice’s latent heat of melting. B) It goes into ice’s latent heat of vaporization. C) It goes into raising the temperature of a small amount of the liquid water, but not the ice. D) It goes into the liquid water’s latent heat of vaporization. 14. You are watching a science fiction movie where people on a space ship are traveling around the universe observing stars with different temperatures. Which of the following stars has the highest surface temperature? A) A bluish star B) A yellowish star C) A green star D) A reddish star 15. Why is tungsten most often used as the filament in light bulbs? A) It burns hotter than other materials. B) Its emissivity is very high. C) It does not expand much at high temperatures. D) It sublimes slowly at high temperatures.



16. Why is it possible for a blue star to be dimmer than a red star at the same distance from us? A) The blue star is reflecting more light. B) The red star is hotter than the blue star. C) The blue star could have less surface area. D) The blue star could have more surface area. 17. What does a heat pump not do? A) Increase entropy B) Move heat from a low temperature region to a high temperature region C) Perform work on its surroundings D) Conserve energy 18. “The entropy of an isolated system never decreases.” Which Law of Thermodynamics is this? A) Zeroth B) First C) Second D) Third 19. Which of the following quantities is conserved? A) Energy B) Heat C) Entropy D) Force 20. In a car engine, the compression stroke involves the piston compressing the air/gas mixture so rapidly that virtually no heat loss can occur. In the compression stroke, the air/gas mixture A) heats because of friction between the gas and the cylinder. B) heats because of friction between the gas and air molecules. C) heats because work is being done on the air/gas mixture. D) cools because the air/gas mixture is doing work on the piston. 21. The “strokes”, or “cycles” in a four – stroke engine are A) induction, compression, power, exhaust B) ignition, compression, power, exhaust C) ignition, induction, power, exhaust D) vacuum, compression, ignition, exhaust



22. You are working late in the physics lab, where you measure the period of a pendulum to be 0.8 s. You fall asleep and have a dream that you are on a planet whose gravitational strength is 4 times that of the earth. If your dream is to be physically accurate, the period of the pendulum in your dream must be A) 0.8 s. B) 0.4 s. C) 1.6 s. D) 3.2 s. 23. You decide to attend an amusement park which has a ride where you are strapped into a chair which is in turn firmly attached to a plastic cable. You are released and you bounce up and down as a harmonic oscillator—a mass on the end of spring. Next in line is somebody who weighs twice as much as you do. When the heavier person goes on the ride, you notice that A) both of you will have the same period, regardless of how high you bounce. B) the heavier rider will have a longer period than the lighter one. C) the two riders will have the same period, as long as the height of their bounces are the same. D) the heavier rider will have a shorter period than the lighter one. 24. Which Law of Thermodynamics relates change in internal energy to heat added to a system and work done by it? A) Zeroth B) First C) Second D Third 25. It is a hot summer day and your friend's apartment has no air conditioning. However, a brand new refrigerator lies unopened in the center of the living room. Being a creative person, your friend closes all the doors and windows of the apartment, unpacks the refrigerator, plugs it in, and turns it on. Your friend then opens the refrigerator door and uses a small fan to circulate the air past the refrigerator and throughout the room. After the refrigerator has operated for a few minutes, the average temperature in the room is A) lower than it was before. B) higher than it was before. C) the same as it was before and the temperature is uniform throughout the room. D) the same as it was before, but some regions are hotter and others are colder. 26. Suppose you have a gas which gives up heat energy as it does work on its surroundings. Must the temperature of the gas increase, decrease or can you not determine how the temperature will behave? A) Increase B) Decrease C) Stay the same. D) Cannot tell from the information provided.



27. A thermoelectric cooler is a type of heat pump that uses electric power to move heat against its natural direction of flow. In other words, it transfers heat from something cold to something hot. In such a heat pump A) input electricity provides electrons that carry the heat. B) Newton's laws of motion prevent heat from moving from a cool region to a warm region. C) input power is required because the flow of heat from a cool region to a warm region alone would decrease the entropy (disorder) of the system. D) input power is required because the flow of heat from a cool region to a warm region alone would violate the conservation of energy. 28. When water freezes into ice cubes in your freezer, the water goes from being disordered to being relatively ordered. Why does this process not violate the 2nd law of thermodynamics? A) The ice is less dense than the liquid water. B) Although ordered, the entropy of the ice is greater than the entropy of the liquid water. C) This process does violate the 2nd law of thermodynamics. D) When we consider the entire refrigerator and the room it is located in, the entropy has increased. 29. The surface of the moon is exposed to full solar radiation because it has no atmosphere. Why then does the moon not heat up endlessly until it disintegrates? A) Convection in the soil carries energy away. B) Its temperature rises until it is able to radiate heat away into space as fast as it arrives from the sun. C) It has disintegrated but the light just hasn’t reached us yet. D) Because the moon is isolated from the sun by empty space, the sun's heat can't reach it (only light can) and the moon doesn’t experience any changes in temperature. 30. In Discovery room #6, you dipped a thermocouple into alcohol and then held it up in the air. What happened to the temperature reported by the thermocouple? A) It stayed the same because the alcohol was at room temperature. B) It went up because the alcohol raised the latent heat of vaporization in order to evaporate. C) It went up because of convection currents carrying the alcohol away from the thermocouple. D) It went down because the heat from the alcohol goes into the latent heat of vaporization, lowering the temperature of the alcohol. 31. Which of the following would be a valid way to improve the efficiency of an internal combustion engine? A) Compress the fuel–air mixture more to raise the temperature if the ignited gas. B) Add more fuel to the mixture to make the engine run faster. C) Compress the fuel–air mixture less to allow more fuel into the chamber before ignition. D) Cool the engine to a lower temperature so that less heat is lost in the cycle.



32. Your dryer is broken, so you have to hang your wet clothes from the washing machine outside to dry. Under which conditions would your clothes dry fastest? A) When it is 50°F with 50% relative humidity. B) When it is 75°F with 50% relative humidity. C) They will dry at the same rate at any temperature with 50% relative humidity. D) The clothes will not dry with 50% relative humidity. 33. Which is true about steam at 100° C versus water at 100° C? A) Steam at 100° C contains more energy per kilogram than water at 100° C. B) Water at 100° C contains more energy per kilogram steam at 100° C. C) They both contain the same amount of energy per kilogram. D) Water only contains more energy per kilogram than steam on the Kelvin temperature scale. 34. An incandescent light bulb that has operated for a long time will have a dark spot on the top of the bulb. This dark spot is evidence that the bulb contains inert gas because the dark spot forms when A) the inert gas carries light downward from the top of the bulb so that it can be emitted by the filament. B) the buoyant force of the inert gas lifts the filament upward so that it brushes against the top of the bulb. C) convection in the inert gas carries filament atoms up to the top of the bulb. D) microwaves from the filament heat the inert gas and produce light, along with overheating the glass near the top of the bulb. 35. If you double the absolute temperature of a light bulb filament, its power output increases by a factor of A) 2 B) 4 C) 8 D) 16 36. You're riding on a pogo stick–a vertical stick with a spring at the bottom and foot pads on which you stand. You're holding the top of the stick tightly in your hands, and you and the stick are bouncing up and down on its spring. As you land after one particularly high bounce, the spring becomes more and more tightly compressed. When the spring is at half its maximum compression, your velocity is A) downward and your acceleration is upward. B) upward and your acceleration is downward. C) downward and your acceleration is downward. D) upward and your acceleration is upward.



37. You have always wondered how much one of your friends weighs and devise a scheme to measure his weight secretly. You have him sit in a tubular steel chair. This popular style of chair consists of a single steel tube that is bent into a frame and that supports a seat bottom and a back. The empty chair weighs 10 pounds and is 30 inches tall. The frame acts as a spring and bends downward slightly when the chair is occupied. When you sit properly in the chair yourself, it bends downward 1 inch. When your friend sits properly in the chair, it bends downward 2 inches. From that observation, you know that your friend weighs about A) one-half as much as you do. B) twice as much as you do. C) four times as much as you do. D) one-third as much as you do. 38. You are riding an amusement park ride where you are strapped to the inside of a giant metal wheel that is rotating quite rapidly. Your acceleration is A) away from the center of the wheel. B) straight down. C) toward the center of the wheel. D) straight up. 39. Wind is can be one of nature’s ways of transferring energy through A) conduction. B) convection. C) transmission. D) radiation. 40. A sea lion balances a ball on the tip of his nose and holds his head perfectly still. This is an example of

A) dynamic equilibrium. B) stable equilibrium. C) unstable equilibrium. D) neutral equilibrium. 41. Solid nitrogen has a greater density than liquid nitrogen. You put a block of solid nitrogen into a container of liquid nitrogen. What happens? A) The solid nitrogen floats in the liquid nitrogen. B) The liquid nitrogen sublimes. C) The solid nitrogen sinks in the liquid nitrogen. D) The liquid nitrogen boils.



42. You are in the kitchen with three mixing bowls in front of you. One bowl is metal, the second is glass and the third is plastic. All three are at exactly the same temperature: the 20° C temperature of the room. If you touch the three bowls together,

A) heat will flow from the plastic bowl to the glass bowl, and from the glass bowl to the metal bowl. B) heat will flow from the metal bowl to the glass bowl, and from the glass bowl to the plastic bowl. C) no heat will flow because the glass and plastic are poor heat conductors. D) no heat will flow between the bowls. 43. A flashlight equipped with new batteries produces bright, yellow-white light. As the batteries in the flashlight wear out, the bulb will A) suddenly go out even if the filament doesn't break. B) glow dimly and produce reddish light. C) continue to glow brightly, but produce redder light. D) glow dimly, but continue to produce yellow-white light. 44. Moments before it is ignited by the sparkplug, the mixture of fuel and air inside an automobile cylinder is compressed to very high density. During the compression process, the mixture’s

A) temperature stays the same but its pressure rises. B) temperature rises dramatically and so does its pressure. C) temperature drops dramatically but its pressure rises. D) temperature rises dramatically but its pressure drops. 45. You place three nonflammable objects in a fire. They are identical in shape and size, but one object is black, the second is white, and the third is shiny silver. After a few minutes, all three objects are at the same temperature: 1800° C. They remain solid and are now glowing with thermal radiation. Which one is glowing most brightly? A) The black object. B) They are all glowing with equal brightness. C) The silver object. D) The white object.


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physics exam 2007