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PHYSICS 2A FINAL EXAM May 25, 2001 Name:___________________ Rules for Exam: 1. Show your work on numerical problems. Do not expect any credit for a problem if I cannot logically follow what you have put on your paper. 2. Make sure you include units with each answer. One point will be deducted for each infraction. 3. Points will be deducted for students that refuse to turn in their exams, when asked to do so (at the end of class). 4. In general you will not be penalized for incorrect sig. figs. However, one point will be deducted for each answer that has a ridiculous amount of significant figures. For example, a final answer quoted as 2.239389479 m/s is ridiculous. 5. Circle your final answers. There are 12 pages to this exam. Put your name on all pages of the exam. Good Luck! ________________________________________________________ Conversion Factors: Lv water 2.26x106J/kg Specific heat of water 4186J/kgoC Specific heat of steam 2010J/kgoC 1 cm= 10 mm (exact) 1Pa=1N/m2 Lf water 3.34x105J/kg Specific heat of ice 2090J/kgoC 1 km=1000 m (exact) R=8.314J/K-mol=0.0821l-atm/mol-K 1atm=1.013x105 N/m2 Acceleration due to gravity =9.80m/s2= 32.1 ft/s2 downward Scores Part I ___________(out of 56) Part II 1.________ 2.________ 3._________(out of 40 points) Part III-Indicate the short problems you want graded here______________ Indicate the long problem you want graded here____________ 1.________ 2.__________ 3.__________ (out of 55 points) Total __________(out of 151 points) Percentage __________(out of 140 points) Physics 2A Final Exam 10/27/09 PART I- Conceptual Questions Fill in the blank, short answer, and multiple choice. (Unless otherwise noted, all questions are worth 2 points each) 1. Identify the physical quantities (listed choices (1 point per correct answer). Mass Work Speed Torque Force Displacement Weight Acceleration below) that are scalars. Draw a circle around your Energy Momentum Temperature Time Impulse Spring Constant Velocity Specific Heat 2. Archimedes’ principle states that a. the buoyant force acting on an object is equal to the weight of the displaced fluid. b. the buoyant force acting on an object is equal to the mass of the displaced fluid. c. the buoyant force acting on an object is equal to 0 if the object sinks to the bottom surface of its container. d. the buoyant force acting on an object is equal to the 0.5 times the weight of the displaced fluid. e. the buoyant force acting on an object is always equal to the weight of the object itself. 3. For every action there is an equal and opposite reaction is a statement of a. Newton’s 1st Law b. Newton’s 2nd Law c. Newton’s 3rd Law d. Conservation of energy 4. A measure of inertia is called a. mass b. weight c. force d. displacement 5. The work done by the net force is equal to an object’s a. change in displacement b. change in potential energy c. change in kinetic energy d. change in mass 6. A heat engine requires 3000J of heat from a hot reservoir and rejects 2000J into a cold reservoir. Its efficiency is (3 points) a. 67% b. 44%. c. 33%. d. 22% 7. The transfer of heat by convection will occur a. only in metals. b. only in a vacuum. c. only in non-metallic solids. d. with or without the presence of matter. e. only in the presence of a liquid or gas. 8. A unit of weight is _______________________. 1 Physics 2A Final Exam 10/27/09 Name:_______________________ 9. You are using a wrench and trying to loosen a rusty nut. Which of the arrangements shown is most effective in loosening the nut? List in order of ascending efficiency (least efficient to most efficient) the following arrangements If there are any ties, indicate them: (4 points) ___________________________________________ 10. Suppose you are designing a highway. To increase its strength you reinforce the concrete by embedding steel rods in the concrete. How should the average coefficients of linear expansion for the two materials compare? a. the coefficient of linear expansion of the steel rod must be greater than that of concrete. b. the coefficient of linear expansion of the steel rod must be less than that of concrete. c. the coefficient of linear expansion of the steel rod must be equal to that of concrete. 11. Consider a vibrating string that makes a sound wave that moves through the air. As the guitar string moves up and down, the air molecules that are a certain distance from the string will move: a. up and down b. toward and away from the guitar string c. back and forth along the direction of the length of the string. d. in circles around the guitar string 12. A car is moving at 35m/s approaches a stationary whistle that emits a 220 Hz sound. The speed of sound is 343 m/s. What is the frequency of sound heard by the driver of the car (3 points)? a. 198Hz b. 220Hz c. 242Hz d. 340Hz 13. The rate in which heat is conducted through a material does not directly depend on a. The length of the object. b. The cross sectional area of the object. c. The temperature difference between the ends of the material. d. The mass of the material. 14. A baseball catcher throws a ball vertically upward and catches it in the same spot when it returns to his mitt. At what point in the ball’s path does it experience zero velocity and non-zero acceleration at the same time? a. midway on the way up c. the instant it leaves the catcher’s hand b. at the top of its trajectory d. the instant before it arrives in the catcher’s mitt 2 Physics 2A Final Exam 10/27/09 15. When a sine wave is used to represent a sound wave, the crest corresponds to: a. rarefaction b. condensation c. point where molecules vibrate at a right angle to the direction of wave travel d. region of low elasticity 16. Which of the following best describes the property of the period of orbital revolution for an Earth satellite? a. greater when the orbital radius is smaller b. greater when the orbital radius is larger c. independent of the orbital radius d. determined mainly by the satellite’s mass 17. A speaker generates a continuous tone of 440 Hz. In the drawing, sound travels into a tube that splits into two segments, one longer than the other. The sound waves recombine before being detected by a microphone. The speed of sound in air is 339 m/s. What is the minimum difference in the lengths of the two paths for sound travel if the waves arrive in phase at the microphone (3 points)? a. 0.10m b. 0.39m c. 0.77m d. 1.11m e. 1.54m 18. Draw a schematic representation of a heat engine, indicating both reservoirs, the engine, the flow of heat, and QH, QC,TH, and Tc (6 points). See instructor 19. You are standing on a railroad car that is moving to the left. You throw a ball toward the right. Draw a free-body diagram indicating all the forces acting on you. (5 points). See instructor 2. a 3. c 4. a 5. c 6. c 7. e 8. N, lb or dyne 3 Physics 2A Final Exam 9. 3, (1,4)tie, 2 10. c 11.b 12. c 13. d 14. b 15. a 16. b 17. c. 10/27/09 4 Physics 2A Final Exam 10/27/09 Name:_______________________ Part II-Problems from Chapters 13, and 14 1. A 1.0-kg mass is attached to a spring having a spring constant of 256N/m. The mass is on a frictionless horizontal table. At t=0s, the spring is stretched 25cm to the right of its equilibrium position and released. a. Determine the amplitude of oscillation and the angular frequency  points). Not covered in 2A b. Write an equation that represents its position, x, as a function of time (3 points). c. Determine the period of oscillation of the mass (3 points). d. What are its total energy, its maximum speed, and maximum acceleration (9 points)? 5 Physics 2A Final Exam 10/27/09 2. A listener triples the distance from a source that emits sound uniformly in all directions. By what factor does the intensity change? By how many decibels does the intensity change (10 points)? Not covered in 2A 3. The figures show standing waves of sound in six organ pipes of the same length. Each pipe has one end open and the other end closed. Note: some of the figures show situations that are not possible. a. Which figures do not illustrate possible resonant situations (2 points)? Not covered in 2A b. Which one of the pipes is resonating in its third harmonic (2 points)? c. If the length of the pipes is 0.500 m, what is the frequency of the sound emitted from pipe 3? The speed of sound is 343 m/s (6 points). 6 Physics 2A Final Exam 10/27/09 Name:_______________________ Part III- Comprehensive Problems Shorter Problems-do two of the five problems: Clearly indicate the problems you want graded on the first page. Otherwise, the first two will be graded. (15 points each) 1. Sketch as (accurately as you can) the velocity versus time graph for an object whose velocity is a constant 3m/s for the first 3 seconds, and then decreases at a constant rate for next 3 seconds such that its final velocity is –3m/s. Then sketch (accurately as you can) a graph of its position as a function of time, and its acceleration as a function of time. Assume the object starts from rest and its initial position is 0 meters. How can the acceleration of the object be determined from the velocity vs. time graph? See instructor 7 Physics 2A Final Exam 10/27/09 2. David is using a sling to whirl a 325-gram rock in a horizontal circle at a constant speed. His plan is to release the sling to send the rock toward his nemesis Goliath. When the rock is released, it is initially traveling in the horizontal direction. The radius in which the rock is whirled is 0.70 m. David is standing on a cliff. The rock is thrown from a distance of 22.0 m above ground. His target, Goliath is 40.0 m from David. If the rock hits Goliath in the head, which is 2.4 m above the ground, find (draw a picture here if you would like) a. the elapsed time between the release of the rock and the impact of the rock on Goliath’s head (5 points). 2.0s b. the initial velocity of the rock (4 points). 20m/s c. the centripetal acceleration of the rock when it was whirled in the horizontal circle (4 points). 571m/s/s d. the work done by the centripetal force on the rock when it was whirled around in a horizontal circle.(use the definition of work) zero Joules 8 Physics 2A Final Exam 10/27/09 Name:_______________________ 3. Frozen waste from airplane toilets is routinely ejected at high altitude. Ordinarily it breaks up and disperses over a large area, but sometimes it holds together and strikes the ground. Let's assume a 20.0-kg parcel of frozen waste (at 0oC) is released from an altitude of 12km. When released its initial velocity is 250m/s. As a result of non-conservative forces, the parcel strikes the ground at 100m/s. a. Calculate the work done by non-conservative forces (9 points) -2.88x106J b. Using the result from part (a) calculate mass of frozen waste that can be melted by the conversion of kinetic and gravitational potential energy into heat. Assume that the latent heat of fusion and vaporization are 3.34x105J/kg and 2.26x106J/kg, respectively (6pts). 8.61 kg melts, the rest of it leaves a big mess 9 Physics 2A Final Exam 10/27/09 4. A 29.4-kg sled is pulled up a hill. The coefficient of kinetic friction between the sled and the hill is 0.18. The angle of the hill with respect to the horizontal is 10º. The applied force is parallel to the direction of its displacement. Draw a picture for your benefit. a. How much work is done by gravity if the sled is pushed a distance of 5.7-m (6 points)? -285J b. Calculate the magnitude of the force (applied parallel to the hill) that must be applied to the sled if the velocity of the box is constant over the 5.7-m distance it travels. (9 points) 101N 10 Physics 2A Final Exam 10/27/09 Name:_______________________ 5. Calculate the energy that is required to convert 25 grams of ice at –250K to water at 373K. Assuming that the change in volume of the ice in negligible, calculate its change in internal energy. 20kJ 11 Physics 2A Final Exam 6. 10/27/09 Long Problems-do one of the two problems: Clearly indicate the problem you want graded on the first page. Otherwise, the first one will be graded. (25 points) 1. A 12g bullet is fired into a 2.38 kg block that is hanging by a 1.00 m long string. The bullet block system swings through an angle of 60 degrees when it reaches its maximum height. a. Calculate the initial velocity of the bullet. (12 points) 620m/s b. Calculate the tension in the string when the system makes an angle of 60 degrees with respect to the vertical. You must include a free-body diagram with your solution (13 points) 11.7N 12 Physics 2A Final Exam 10/27/09 Name:_______________________ 2. A lunch tray is being held in one hand, as shown in the drawing. The mass of the tray itself is 0.200kg, and its center of gravity is located at its geometrical center. On the tray are a 1.00 kg plate of food and a 0.250kg cup of coffee. Obtain the force T exerted by the thumb and the force F exerted by the fingers. Both forces act perpendicular to the tray, which is being held parallel to the ground. Don’t forget to include a free-body diagram (25 points). F=70.6N T=56.4N 13