Exam2_2112_SP23_Blank

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Louisiana State University *

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2112

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Physics

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Dec 6, 2023

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PHYSICS-2112 Spring 2023 Exam 2A March 21, 2023 Last Name (print) First Name (print) Signature LSUID No. TURN OFF AND PUT AWAY ANY AND ALL NONAPPROVED ELECTRONIC DEVICES. You may only use an ordinary scientific or graphing calculator. You may not use a cell phone, smart phone, or tablet application as your calculator. Examine your paper to be sure it is complete and legible. There should be 12 multiple choice questions and 2 free-response problems, totaling 100 points. There are five (5) pages, including the cover sheet. For the multiple choice questions , bubble in the correct answer on your ScanTron for each question. There is room on the exam for scratch work or calculations, but that work will not be checked or graded. Partial credit may be awarded on multiple choice questions, but this partial credit will be based on the answers that you have bubbled in on the ScanTron and NOT on your scratch work on the exam itself. For the free-response problems, show all relevant work in the space provided. Without supporting work, even a correct answer will receive little or no credit. Partial credit will be awarded as warranted. If your work for a problem is somewhere other than the space provided for that part of the problem, you must indicate where your work is located . E.g ., if you need more room for your solution, then you may write on the back of the page. Be sure to add a note to this effect; otherwise, anything on the back of the paper will be regarded as scratch work and w ill not be checked or graded. Be sure that numerical answers appear with appropriate SI units . Points will be deducted for missing, incorrect, or "silly" units. If the final answer is, in fact, a dimensionless quantity, please write the numerical result followed by the word dimensionless . Your free response will be graded for consistency. That is, if you need a quantity from a previous part and didn’t get it right or could not complete it you will be graded on your work for the part you are working on. Circle one: Vekhter (Sec. 1; MWF 10:30 am) Marley (Sec. 2; TTh 9:00 am)

Question #1 Bubble in the answer choice corresponding to your class section number. A) Sec. 1; MWF 11:30 am C) Sec. 2; TTh 9:00 am Question #2 Your version of the test is A. Bubble in answer A on your ScanTron. Question #3 (5 points) A sinusoidal wave with the wave number k=2 m -1 travels along a string. The time for a particular point to move from zero to maximum displacement is 0.5 s. What is the wave speed v ? A) v = 1 m/s B) v =1.57 m/s C) v = 2 m/s D) v =3.14 m/s E) v =6.28 m/s Question #4 (5 points) Suppose that a simple pendulum consists of a small 25 g bob at the end of a cord of negligible mass. If the angle θ between the cord and the vertical is given by θ = (0.06 rad) cos[ (7 rad/s ) t + 0.78 rad] , what is the pendulum's length? A) 1.40 m B) 1.23 m C) 0.71m D) 0.20 m E) none of the above, a different length Question #5 (5 points) What is the maximum acceleration of a ball that oscillates on a spring with an amplitude of 3 cm at a frequency of 7.6 Hz? A) 5.44 m/s 2 B) 14.3 m/s 2 C) 22.8 m/s 2 D) 68.4 m/s 2 E) 2.53 m/s 2

Question #6 (5 points) Two sinusoidal waves, identical except for phase, travel in the same direction along a string, producing a net wave y (x, t) = (2.80 mm) sin(21.0x - 5.30t + 0.510 rad) with x in meters and t in seconds. What is the amplitude of each of the original waves? A) 1.37 mm B) 0.71 mm C) 1.40 mm D) 1.60 mm E) 14.84 mm Question #7 (5 points) If two sources emit sound waves of the of the same amplitude with the same frequency and phase, and an observer is placed so that the distance to one of the sources is 3.1415 wavelengths shorter than the distance to the other source, what type of interference will occur? A) fully constructive B) fully destructive C) intermediate but closer to fully constructive D) intermediate but closer to fully destructive E) depends on the frequency of the sound wave Question #8 (5 points) If you have a point source of sound, what is the change in the sound level when you double the distance to the source? A) 2dB B) 3dB C) 4dB D) 6dB E) none of the above Question #9 (5 points) Organ pipe A (closed at one end, open at the other) is three times as long as a pipe B open at both ends. The ratio of their second lowest frequencies, f A /f B , is A) 1:4 B) 1:3 C) 1:2 D) 3:1 E) 4:1 A B

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