EF 152 Exam 2 - Fall, 2016 Page 1 Copy 223

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1 EF 152 Exam 2 - Fall, 2016 Page 1 Copy 223 Instructions Do not open the exam until instructed to do so. Do not leave if there is less than 5 minutes to go in the exam. When time is called, immediately stop writing, remain seated, and pass your exam to the center aisle. Working after time is called results in an automatic 10 point deduction. Turn your equation sheets in with your exam. Guidelines Assume 3 significant figures for all given numbers unless otherwise stated Show all of your work no work, no credit Write your final answer in the box provided Include units for all answers Harmonic Motion ω angular frequency A amplitude k stiffness m mass δ phase angle x 0 initial displacement v 0 initial velocity T period f frequency sin sin cos cos cos sin sin sin cos tan Wave Equation wave velocity amplitude wave number angular frequency wavelength frequency 2, cos is positive if sign of is negative. Parallel Axis Theorem Pendulums simple: physical: Speed of Sound Bulk Modulus mass density Speed of Sound in Air: 331.6m/s m/s Natural frequencies λ wavelength L Length n harmonic T tension μ mass per unit length f frequency v wave velocity in medium String: Air Columns: ( in ) ( in ) closed 1, 3, 5, open 1,2,3, Wave Speed: Cables, Ropes, etc. Tension mass per unit length Modulus of elasticity mass density Transverse: Longitudinal: Sound Level in db 10 log Intensity reference intensity, 110 W/m Doppler Shift frequency shifted frequency velocity of sound in medium velocity of listener velocity of source Beat Frequency: + listener to source Wave Energy, Power, Intensity energy intensity power average power cos 4 Light Waves Law of Reflection: Index of refraction: Snell s Law: sin sin Light wavelength: Total Internal Reflection: sin speed of light in vacuum: 310 m/s

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3 EF 152 Exam 2 - Fall, 2016 Page 3 Copy 223 Name: Section: A102 11:10 Michael B102 12:40 Michael C102 2:10 Michael 1. Write your name and section above. Specify your EXAM ID below. Use 000 if you don t know your exam ID. Per 102 Per 216 Per 217 A216 Karen. B216 Karen C216 Karen Digit #1 Digit #2 Digit #3 A217 Stefy 4. (2 pt) A sound wave passes from air into water. Of the three properties, frequency, wavelength, and wave speed, which will change? Only Frequency Only Wavelength Only Wave Speed Frequency and Wavelength Wave Speed and Wavelength 5. (2 pt) Dr. Biegalski s voice has a higher pitch after inhaling helium. Which of the following is a true statement about the speed of sound, v, in the two different materials: helium and air? vair > vhelium vair < vhelium vair = vhelium 6. (2 pt) A sound wave resonates in a tube of length L with two open ends. What are the wavelengths of the three lowest resonating frequencies generated in the tube? L, 2L, 3L 2L, L, 2L/3 L/2, L/3, L/5 L/3, L/5, L/7 4L, 4L/3, 4L/5 7. (2 pt) The 8th harmonic of a pipe with two open ends is 2000 Hz. Determine the frequency of the 2nd harmonic. 250 Hz 500 Hz 750 Hz 1000 Hz 8. (3 pt) A 2.5 m string has an 8 th harmonic with a frequency of 464 Hz. Find the speed of the wave in the string. 580 m/s 290 m/s 145 m/s m/s

4 EF 152 Exam 2 - Fall, 2016 Page 4 Copy (3 pt) Two strings of different lengths and different tensions have the same mass per unit length and the same fundamental frequency. If string 1 has twice the tension as string 2, what is the value of the second string length, L2? (3 pt) A tube of length L1 is open at both ends. A second tube of length L2 is closed at one end and open at the other end. This second tube has the same fundamental frequency as the first tube. What is the value of L2? (3 pt) A quiet radio has an intensity level of about 40 db. Busy street traffic has a level of about 70 db. How much greater is the intensity of the street traffic compared to the radio? About times About the same About 10 times About 100 times About 1000 times 12. (10 pt) The displacement (in meters) of a wave is y (x,t) = 0.26 cos ( 4 t 12 x) where t is in seconds and x is in meters. Determine the speed of propagation. (HINT not the velocity of a particle). 13. (10 pts) Two students listen to Prof Schleter playing trombone. One student is 160 meters from the trombone. The other student is 40 meters from the trombone. What is the difference between the sound intensity levels (in db) heard by the two students?

5 EF 152 Exam 2 - Fall, 2016 Page 5 Copy (15 pts) Dr Biegalski hangs a 0.25 kg tennis racket from the end of its handle and it oscillates with a period of 1.42 seconds. If the mass moment of inertia about its center of mass is kg m 2, determine the location of the center of mass of the tennis racket from the end of the handle. (Assume small angle approximation applies) r CM 15. (15 pt) An object is in simple harmonic motion and has a maximum displacement of 0.08 meters and a maximum acceleration of 65 m/s 2. The initial displacement is 0.03 m. Determine the magnitude of the initial velocity.

6 EF 152 Exam 2 - Fall, 2016 Page 6 Copy (15 pts) The speed of sound in blood is 1540 m/s. A stationary Doppler blood flow meter emits ultrasound waves at a frequency of 5.0 x 10 6 Hz. Blood flows away from the emitter at 0.15 m/s. What is the beat frequency detected by the meter? 17. (15 pts) A graduate student floats motionless on a raft in a 1.2 m deep swimming pool and sees an object at Point S on the bottom of the pool. What is the horizontal distance, H, between the student and the object? H 0.3 m n = m