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Physics 124 – 2009 Final Exam, Exams of Physics

A final exam for physics 124 from 2009, including multiple-choice questions on various topics such as mechanics, thermodynamics, and waves. Useful physical constants and formulae are provided.

Typology: Exams

2012/2013

Uploaded on 02/08/2013

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Physics 124 2009 Final
4-7 PM, Tuesday May 12, 2009, College Ave Gym
Your name sticker
with exam code
1. The exam will last 3 hours, from 4 - 7 PM. Use a #2 pencil to make entries
on the answer sheet. Enter the following ID information now, before the
exam starts.
2. In the section labelled NAME (Last, First, M.I.) enter your last name, then
fill in the empty circle for a blank, then enter your first name, another
blank, and finally your middle initial.
3. Under STUDENT # enter your 9-digit RUID Number.
4. Under CODE enter the exam code given above.
5. You do not need to enter the course or section number.
6. During the exam, you may use a calculator and are allowed two 8.5 x 11
inch sheets of paper with whatever you want written on them.
7. The exam consists of 30 multiple choice questions. For each multiple choice
question mark only one answer on the answer sheet. There is no deduction
of points for an incorrect answer, so even if you cannot work out the answer
to a question, you should make an educated guess.
8. At the start of the exam, make sure that your copy contains all 30 questions.
Raise your hand if this is not the case, and a proctor will help you. Also
raise your hand during the exam if you have a question.
9. A proctor will check your name sticker and your student ID sometime during
the exam. Please have them ready.
10. You are not allowed to give help to any other student, ask for help from any-
one but a proctor, or change your seat without permission from a proctor.
Doing so will result in a zero score for the exam.
11. Hand in this cover sheet along with your answer sheet.
12. Please sign below to indicate that you have read and understood these in-
structions.
Useful physical constants: Gas constant R= 8.314 J/mol K. Boltzmann con-
stant kB= 1.38×1023J/K. Avogadro’s number NA=R/kB= 6.02×1023.
0C = 273 K. Speed of sound in air = 343 m/s. Atmospheric pressure = 105
Pa. Gravitational constant G= 6.67×1011 m3/s2kg. At earth’s surface g
= 9.8 m/s2. Stefan-Boltzmann constant σ= 5.67×108W/m2K4. Volume
of a sphere = 4πr3/3.
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Physics 124 – 2009 Final

4-7 PM, Tuesday May 12, 2009, College Ave Gym

Your name sticker

with exam code

  1. The exam will last 3 hours, from 4 - 7 PM. Use a #2 pencil to make entries on the answer sheet. Enter the following ID information now, before the exam starts.
  2. In the section labelled NAME (Last, First, M.I.) enter your last name, then fill in the empty circle for a blank, then enter your first name, another blank, and finally your middle initial.
  3. Under STUDENT # enter your 9-digit RUID Number.
  4. Under CODE enter the exam code given above.
  5. You do not need to enter the course or section number.
  6. During the exam, you may use a calculator and are allowed two 8.5 x 11 inch sheets of paper with whatever you want written on them.
  7. The exam consists of 30 multiple choice questions. For each multiple choice question mark only one answer on the answer sheet. There is no deduction of points for an incorrect answer, so even if you cannot work out the answer to a question, you should make an educated guess.
  8. At the start of the exam, make sure that your copy contains all 30 questions. Raise your hand if this is not the case, and a proctor will help you. Also raise your hand during the exam if you have a question.
  9. A proctor will check your name sticker and your student ID sometime during the exam. Please have them ready.
  10. You are not allowed to give help to any other student, ask for help from any- one but a proctor, or change your seat without permission from a proctor. Doing so will result in a zero score for the exam.
  11. Hand in this cover sheet along with your answer sheet.
  12. Please sign below to indicate that you have read and understood these in- structions.

Useful physical constants: Gas constant R = 8.314 J/mol K. Boltzmann con- stant kB = 1.38× 10 −^23 J/K. Avogadro’s number NA = R/kB = 6.02× 1023. 0 ◦C = 273 K. Speed of sound in air = 343 m/s. Atmospheric pressure = 10^5 Pa. Gravitational constant G = 6.67× 10 −^11 m^3 /s^2 kg. At earth’s surface g = 9.8 m/s^2. Stefan-Boltzmann constant σ = 5.67× 10 −^8 W/m^2 K^4. Volume of a sphere = 4πr^3 /3.

  1. If you put a uniform block at the edge of a table, the center of the block must be over the table for the block not to fall off. Now you stack two identical blocks at the table edge (see the Figure). In terms of the length L of each block, what is the maximum overhang possible?

a) L/ 2 b) 3 L/ 4 c) L d) 5 L/ 4 e) 3 L/ 2

  1. A runner of mass 60 kg runs around the edge of a horizontal turntable mounted on a vertical frictionless axis through its center. The runner’s velocity relative to the earth has magnitude 3 m/s. The turntable is rotating in the opposite direction with an angular velocity of magnitude 0.2 rad/s relative to the earth. The radius of the turntable is 3 m, and its moment of inertia about the axis of rotation is 85 kg·m^2. Find the final angular velocity of the system if the runner comes to rest relative to the turntable. (You can treat the runner as a particle.) a) 0 rad/s b) 0.12 rad/s c) 0.41 rad/s d) 0.84 rad/s e) 1.5 rad/s
  2. The International Space Station makes 15.65 revolutions per day in its orbit around the Earth. Assuming a circular orbit, how high is this satellite above the surface of the Earth? (The mass of the Earth is 6× 1024 kg, its radius 6.38× 106 m, the gravitational constant 6.67× 10 −^11 N·m^2 /kg^2 ). a) 110 km b) 380 km c) 510 km d) 790 km e) 1200 km
  1. Water flows steadily from an open tank as in the figure. The elevation of point 1 is 10 m, and the elevation of points 2 and 3 is 2 m. The cross- sectional area at point 2 is 0.040 m^2 ; at point 3 it is 0.020 m^2. The area of the tank is very large compared with the cross-sectional area of the pipe. What is the speed of flow at point 2?

a) 3.1 m/s b) 6.3 m/s c) 12 m/s d) 25 m/s e) 37 m/s

  1. A rope of length 1.46 m is stretched between two supports with a tension that makes the transverse waves have a speed of 47.1 m/s. What is the frequency of the fundamental harmonic? a) 1 Hz b) 2 Hz c) 4 Hz d) 8 Hz e) 16 Hz
  2. Two loudspeakers, A and B, are driven by the same amplifier and emit sinusoidal waves in phase. The frequency of the waves emitted by each speaker is 694 Hz. You are standing between the speakers, along the line connecting them and are at a point of constructive interference. How far must you walk toward speaker B to reach the first point of destructive interference? (Assume that the speed of sound in air is 344 m/s). a) 0.12 m b) 0.25 m c) 0.37 m d) 0.50 m e) 0.62 m
  1. One mole of Hydrogen gas and half a mole of Helium gas are mixed together in a container and maintained at a fixed temperature T. How does the pressure PH exerted by the hydrogen gas compare to the pressure PHe exerted by the helium molecules? Note that an atom of helium has twice the mass of an H 2 molecule. a) PH = 2PHe b) PH =

2 PHe c) PH = PHe d) PH = 2PHe/

e) PH = PHe/ 2

  1. We start with 5 moles of an ideal monatomic gas with an initial temperature of 131◦C. The gas expands and, in the process, absorbs an amount of heat equal to 1280 J and does an amount of work equal to 2040 J. What is the final temperature of the gas? a) 119 ◦C b) 125 ◦C c) 131 ◦C d) 137 ◦C e) 142 ◦C
  2. A cylinder contains 0.25 mol of carbon dioxide (CO 2 ) gas at a temperature of 27◦C. The cylinder is provided with a frictionless piston, which maintains a constant pressure of 1 atm on the gas. The gas is heated until its temper- ature increases to 127◦C. Note that some work W is done by the gas in this process. Assume that the CO 2 may be treated as an ideal polyatomic gas with three translational degrees of freedom and three rotational degrees of freedom. How much heat Q was supplied to the gas? a) 208 J b) 310 J c) 625 J d) 830 J e) 1210 J
  1. An ideal gas is held in a container of volume V at pressure P. The rms speed of a gas molecule under these conditions is v. If now the volume and pressure are changed to 2V and 2P , the rms speed of a molecule will be: a) v b) v/ 4 c) v/ 2 d) 2 v e) 4 v
  2. Which of the following is a TRUE statement about an ideal gas?

a) During an isothermal process, the entropy of the gas does not change. b) During an adiabatic process, the temperature of the gas does not change. c) During an isobaric process, no work is done on or by the gas. d) During an isothermal process, no heat enters or leaves the gas. e) During an isochoric process, the change in the internal energy of the gas is exactly equal to the amount of heat that goes into (or out of) the gas.

  1. When an ideal gas is expanded in volume at constant pressure, the average kinetic energy of the gas molecules a) decreases. b) increases. 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 to make such a determination.
  2. A Carnot engine is operated between two heat reservoirs at temperatures of 520 K and 300 K. If the engine receives 6.4 kJ of heat energy from the reservoir at 520 K in each cycle, how many joules per cycle does it reject to the reservoir at 300 K? a) 0 kJ b) 1.7 kJ c) 2.6 kJ d) 3.7 kJ e) 6.4 kJ
  1. Assume that the total surface area of the human body is 1 m^2 , its surface temperature is 30◦C, and its emissivity e = 1. If the surroundings are at the temperature of 20◦C, what is the net rate of heat loss from the body by radiation? a) 10 W b) 60 W c) 150 W d) 230 W e) 480 W
  2. An aluminum block with mass m = 0.26 kg and an initial temperature TB =362 K is placed into a cup of water with mass M = 0.32 kg and an initial temperature TW =295 K. The values of the specific heat for water and aluminum are 4186 J/(kg·K) and 900 J/(kg·K), respectively. Find the final equilibrium temperature Tf. a) 305 K b) 315 K c) 325 K d) 345 K e) 655 K
  3. Which of the following is a FALSE statement?

a) The difference in entropy between two states of a system is indepen- dent of the path between the two states. b) Entropy can be measured in units of J/K. c) The total entropy change in one cycle of a Carnot engine is zero. d) The entropy of an isolated system is conserved, i.e., constant. e) Entropy is a quantitative measure of disorder.

  1. Why do we ignore work done by solids and liquids?

a) They do not expand/contract. b) There is no pressure inside them. c) Their work is small. d) They don’t do work. e) There is no pressure difference at the surface.

  1. You need to design a power plant that generates 10^9 W of work. En- vironmental considerations limit its waste heat production at a level of 0.5× 109 W. The temperature of the cold reservoir TC = 313 K. What should be the temperature of the hot reservoir, TH , in order to meet these require- ments? a) 273 K b) 373 K c) 451 K d) 612 K e) 939 K
  2. A 15-kg block of ice at 0◦C melts to liquid water at 0◦C inside a large room that has a temperature of 20◦C (disregard further heating of water from 0 ◦C to 20◦C). For water, the heat of fusion is 3.35× 105 J/kg. Treat the ice and the room as an isolated system, and assume that room is large enough for its temperature change to be ignored. Calculate the net entropy change of the system during this process. a) 0 J/K b) -350 J/K c) 350 J/K d) 620 J/K e) 1250 J/K