PHYSICS 221 SPRING FINAL EXAM: May 1, :30pm - 6:30pm

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1 PHYSICS 221 SPRING 2012 FINAL EXAM: May 1, :30pm - 6:30pm Name (printed): Recitation Instructor: Section # INSTRUCTIONS: This exam contains 25 multiple-choice questions plus 2 extra credit questions, each worth 4 points. Choose one answer only for each question. Choose the best answer to each question. Answer all questions. Allowed material: Before turning over this page, put away all materials except for pens, pencils, erasers, rulers and your calculator. There is a formula sheet attached at the end of the exam. Other copies of the formula sheet are not allowed. Calculator: In general, any calculator, including calculators that perform graphing, is permitted. Electronic devices that can store large amounts of text, data or equations (like laptops, palmtops, pocket computers, PDA or e-book readers) are NOT permitted. Wireless devices are NOT permitted. If you are unsure whether or not your calculator is allowed for the exam, ask your TA. How to fill in the bubble sheet: Use a number 2 pencil. Do NOT use ink. If you did not bring a pencil, ask for one. You will continue to use the same bubble sheet that you already used for the first midterm exam. Bubble answers on the bubble sheet for this exam. Please turn over your bubble sheet when you are not writing on it. If you need to change any entry, you must completely erase your previous entry. Also, circle your answers on this exam. Before handing in your exam, be sure that your answers on your bubble sheet are what you intend them to be. You may also copy down your answers on a piece of paper to take with you and compare with the posted answers. You may use the table at the end of the exam for this. When you are finished with the exam, place all exam materials, including the bubble sheet, and the exam itself, in your folder and return the folder to your recitation instructor. No cell phone calls allowed. Either turn off your cell phone or leave it at home. Anyone answering a cell phone must hand in their work; their exam is over. Best of luck, Drs. Soeren Prell and Kai-Ming Ho

2 55) On Earth, when an astronaut throws a kg stone vertically upward, it returns to his hand a time T later. On planet X he finds that, under the same circumstances, the stone returns to his hand in 2T. In both cases, he throws the stone with the same initial velocity and it feels negligible air resistance. The acceleration due to gravity on planet X (in terms of g) is A) 2g B) g/ 2 C) g/4 D) g/2 E) 2g 56) The Ferris wheel in the figure rotates counterclockwise with uniform angular speed. What is the direction of the average acceleration of a gondola as it goes from the top to the bottom of its trajectory? A) Up B) Down C) To the left D) To the right E) The acceleration is 0 because the motion is uniform.

3 57) In the figure, a person pulls horizontally on block B and both blocks A and B move horizontally as one unit. There is friction between block B and the horizontal table. Air resistance is negligible. If the two blocks are moving to the right at constant velocity, A) the horizontal force that B exerts on A points to the left. B) the horizontal force that B exerts on A points to the right. C) B exerts no horizontal force on A. D) the pull force is greater than the friction force E) the pull force is less than the friction force 58) A ball sits at rest on a horizontal tabletop. The weight of the ball is one half of a Newton s third law force pair. Which force is the other half? A) the force of the Earth s gravity on the ball B) the upward force that the table top exerts on the ball C) the upward force that the ball exerts on the Earth D) the downward force that the ball exerts on the table top E) the frictional force between the ball and the table top

4 59) You push a block of weight mg against a wall with force F perpendicular to the wall such that the static friction between the wall and the block barely keeps the block from falling. Consider the friction between your finger and the block negligible and the coefficient of static friction between the wall and the block is µ S. When you push with a force 2F, the magnitude of the friction force will be. A) mg B) 2mg C) µ S F D) 2(µ S F mg) E) µ S mg 60) A small hockey puck slides without friction over the icy hill shown in the figure and lands 6.20 m from the foot of the cliff with no air resistance. What was its speed v 0 at the bottom of the hill? A) 4.71 m/s B) 20.8 m/s C) 13.7 m/s D) 14.4 m/s E) 17.4 m/s

5 61) A 58.0-gram tennis ball is dropped from a height of 2.54m above ground. It hits the floor and bounces back up to a height of 1.40m. Neglecting air resistance, when the ball bounces it imparts on the floor an impulse of magnitude. A) 1.4 kg m/s B) 0.11 kg m/s C) 2.2 kg m/s D) 0.67 kg m/s E) 0.71 kg m/s 62) Two objects of the same mass move along the same line in opposite directions. The first object is moving with speed v. The objects collide, stick together, and move with speed 0.100v in the direction of the velocity of the first object before the collision. What was the speed of the second object before the collision? A) 0.900v B) 1.20v C) 0.800v D) Zero E) 1.10v

6 63) Starting from rest, a small pebble slides down the frictionless inner surface of a spherical bowl starting from a height of 0.2 m above the bottom of the bowl. The radius of the bowl is 1.0 m. Calculate the magnitude of the linear acceleration (in terms of g) of the pebble at the bottom of its trajectory. A) 0.2 g B) 0.4 g C) 0.6 g D) 1.0 g E) Zero 64) A planet is moving around the Sun in an elliptical orbit. As the planet moves from aphelion (farthest point from the Sun) to perihelion (closest point to Sun), the Sun s gravitational force does. A) positive work on the planet at all points between aphelion and perihelion. B) negative work on the planet at all points between aphelion and perihelion. C) positive work on the planet during part of the motion and negative work during the other part with the total work being positive. D) positive work on the planet during part of the motion and negative work during the other part with the total work being negative. E) positive work on the planet during part of the motion and negative work during the other part with the total work being zero.

7 65) Three objects are connected as shown in the figure. The strings and frictionless pulleys have negligible masses, and the coefficient of kinetic friction between the 2.0-kg block and the table is What is the acceleration of the 2.0-kg block? A) 1.8 m/s 2 B) 4.1 m/s 2 C) 3.3 m/s 2 D) 2.6 m/s 2 E) 5.2 m/s 2 66) The angle that a swinging simple pendulum makes with the vertical obeys the equation!(t) = (0.240 rad) cos!" ( 2.85 rad/s)t # $. What is the length of the pendulum? A) 0.83 m B) 1.21 m C) 2.02 m D) 0.15 m E) It cannot be determined from the information given.

8 67) A sewing machine needle moves up and down in simple harmonic motion. The distance between the highest and lowest point of the needle tip is 2.6 cm and the frequency of the motion is 3.2 Hz. What is the maximum speed of the needle? A) 8.2 cm/s B) 21 cm/s C) 4.1 cm/s D) 13 cm/s E) 26 cm/s 68) In designing buildings to be erected in an area prone to earthquakes, what relationship should the designer try to achieve between the natural frequency of the building and the typical earthquake frequencies? A) The natural frequency of the building should be almost the same as typical earthquake frequencies but slightly lower. B) The natural frequency of the building should be almost the same as typical earthquake frequencies but slightly higher. C) The natural frequency of the building should be very different from typical earthquake frequencies. D) The natural frequency of the building should be exactly the same as typical earthquake frequencies. E) The designer does not have to worry about typical earthquake frequencies.

9 69) The sound from a single source can reach point P by two different paths. One path is 20.0 m long and the second path is 21.0 m long. The sound destructively interferes at point P. What is the minimum frequency of the source if the speed of sound is 343 m/s? A) 343 Hz B) 515 Hz C) 686 Hz D) 6860 Hz E) 172 Hz 70) A brass rod is 69.5 cm long and an aluminum rod is 49.0 cm long when both rods are at an initial temperature of 0 C. The rods are placed in line with a gap between them, as shown in the figure. The distance between the far ends of the rods is maintained at cm throughout. The temperature of both rods is raised until the two rods are barely in contact. The coefficients of linear expansion of brass and aluminum are 2.0 x 10 5 K 1 and 2.4 x 10 5 K 1, respectively. The temperature at which contact of the rods barely occurs is closest to A) 560 o C B) 585 o C C) 605 o C D) 630 o C E) 660 o C

10 71) A substance has a melting point of 20 C and a heat of fusion of 1.9 x 10 4 J/kg. The boiling point is 150 C and the heat of vaporization is 3.8 x 10 4 J/kg at a pressure of one atmosphere. The specific heats for the solid, liquid, and gaseous phases are 600, 1000, and 400 J/(kg K), respectively. The quantity of heat required to raise the temperature of 1.00 kg of the substance from 5 C to 129 C is closest to: A) 34 kj B) 120 kj C) 130 kj D) 140 kj E) 160 kj 72) When a fixed amount of a monatomic ideal gas is expanded in volume at constant pressure, the average kinetic energy of the gas molecules. A) increases. B) decreases. C) does not change. D) may either increase or decrease, depending on whether or not the process is carried out adiabatically. E) may or may not change, but insufficient information is given at make such a determination.

11 73) Consider two pistons filled with ideal gases. One piston has a volume of 10 liters and contains 0.5 mol of Xenon gas at atmospheric pressure. The other piston has a volume of 16 liters and contains 1.0 mol of Argon gas at a temperature of 400K. The atomic mass of Argon is 39.9 gram/mol and the atomic mass of Xenon is 131 gram/mol. The ratio of rms speeds v rms (Xenon)/v rms (Argon) of the gas atoms is closest to A) 0.43 B) 5.2 C) 0.81 D) 8.4 E) ) The figure shows a pv diagram for 0.47 mol of gas that undergoes the process 1 2. The gas then undergoes an isochoric heating from point 2 until the pressure is restored to the value it had at point 1. What is the final temperature of the gas? A) 40 o C B) 2 o C C) 130 o C D) 230 o C E) 510 o C

12 75) A glass window pane is 2.6 m high, 2.3 m wide, and 3.0 mm thick. The temperature at the inner surface of the glass is 24 C and at the outer surface 4.0 C. How much heat is lost each hour through the window? (properties of glass: density: 2300 kg/m 3, specific heat: 840 J/kg C, coefficient of linear thermal expansion: (C ) -1, thermal conductivity: 0.80 W/(m C )) A) 1.1 x 10 8 J B) 1.1 x 10 6 J C) 1.1 x 10 5 J D) 32 J E) 320 J 76) A Carnot refrigerator operates between a hot reservoir at 600K and a cold reservoir at 200K. The refrigerator consumes 50 W of power. How much heat is removed from the interior of the refrigerator in 1 hour? A) 180 kj B) 72 kj C) 720 kj D) 7.5 kj E) 90 kj

13 77) A hot piece of iron is thrown into the ocean and its temperature eventually stabilizes. Which of the following statements concerning this process is correct? A) The entropy lost by the iron is equal to the entropy gained by the ocean. B) The ocean gains more entropy than the iron loses. C) The entropy gained by the iron is equal to the entropy lost by the ocean. D) The change in the entropy of the iron-ocean system is zero. E) The ocean gains less entropy than the iron loses. 78) The figure below shows the measured displacement of a mass oscillating at the end of a spring as a function of time. What is the frequency of the oscillations? A) 0.47 Hz B) 0.94 Hz C) 1.2 Hz D) 1.9 Hz E) 2.6 Hz

14 79) In the collisions experiment, you obtained traces of the motion of a puck like the one shown below: This trace is produced by the sparks generated at a rate of 60 sparks per second. The distance between the first and last point in the trace shown above is measured with a standard metric ruler and found to be 3.40 cm. Due to the limitations of the ruler, we can estimate the uncertainty in the reading to be ± 0.5 mm. You may neglect the uncertainty in the spark generator frequency. What is the uncertainty in the speed of the puck? A) ± 0.5 mm/s B) ± 1 mm/s C) ± 3 mm/s D) ± 5 mm/s E) ± 3 cm/s

15 80) A 40-cm 3 closed container filled with air is warmed up while probes are measuring the temperature and pressure inside the container. The results are shown below in a pressure versus temperature graph. As expected, a linear behavior is observed, so a linear fit is performed. Assuming that the air inside the container is an ideal gas, how many moles of air are trapped inside the container? A) moles B) moles C) 0.24 moles D) 0.88 moles E) 1.3 moles

16 81) In the Forces and Motion experiment, a force probe is fixed to a cart that can roll with or without friction on a track. The whole system (probe + cart) is pulled through a hook screwed onto the probe by a light string that goes through a pulley and has a cylindrical weight attached to the other end (see figure). Force probe Pulley Cart Cylinder Which of the following most accurately describes what the probe measures? Note that in some situations, two or more of these forces may have the same magnitude, but it is important to know which force you are really measuring. A) The net force on the cart + probe system B) The net force on the probe alone C) The tension in the string D) The weight of the cylinder that pulls on the system E) The weight of the cart + probe system