Phy 231 Sp 03 Homework 14 Page 1 of 4 14 1A Which one of the following statements is WRONG a A fluid can transmit only longitudinal sound waves whereas a solid can transmit both longitudinal and transverse sound waves b The speed of sound is much slower than the speed of light c The speed of sound in air is closely the same for all wavelengths d Both light and sound can travel through a perfect vacuum e The range of frequencies for normal human hearing is about 20 Hz to 20 000 Hz 14 2A Which one of the following statements is WRONG a The term ultrasound is used to describe sound waves with frequencies greater than about 20 kHz b In a longitudinal wave the particles move back and forth perpendicular to the direction in which the wave is traveling c Ultrasound waves have wavelengths in matter short enough that they can be used to image organs within the human body d Under the right conditions high intensity ultrasound waves can be used to break up tumors e The physics underlying ultrasonic imaging is that ultrasonic waves are partially reflected from a boundary between two materials with differing densities 14 3A A sound pulse is sent down a 0 5 m length of a liquid reflected from the bottom of the container and detected when it returns to the top of the liquid For a round trip of 1 ms about what is the speed of sound in the liquid a 500 m s b 1000 m s c 340 m s d 2000 m s e None of these 14 4A Light travels in vacuum and air at a speed of about 3 x 108 m s Sound travels in air at a speed of about 345 m sec If a lightning bolt that strikes 7 km a little over 4 miles away from you produces both a flash and a thunder clap about how long after the flash do you hear the thunder a 60 sec b 2 sec c 40 sec d 20 sec e You don t have enough information to tell 14 5A A person sitting 10 m from a point source of sound hears sound intensity Io Assuming no reflections and no absorption about what intensity should be heard by a person sitting 20 m from the point source a Io b Io 2 c Io 4 d 2Io e 4Io 14 6A If you make the intensity of a sound wave 1000 times larger you increase the sound level by about a 20 dB b 30 dB c 1000 dB d 3 dB e You can t tell without knowing the absolute magnitude of the sound intensity 14 7A The siren of an ambulance moving East at 35 m s is emitting sound of frequency 500 Hz About what frequency should be heard by a cyclist in front of the ambulance and moving West at 17 m s Take the velocity of sound to be 345 m s a 585 Hz b 550 Hz c 530 Hz d 430 Hz e 470 Hz 14 8A If an ambulance siren is emitting sound of frequency 500 Hz about what is the difference f f1 f2 between the frequencies you should hear when the ambulance is coming toward you at 35 m s f1 and going away from you f2 at the same speed Assume that you are at rest and take the velocity of sound to be 345 m s a 0 Hz b 50 Hz c 75 Hz d 100 Hz e None of these is close 14 9A Which one of the following statements is WRONG a Increasing the intensity of a sound wave 100 times increases the sound level by 20 dB b In the Doppler effect the frequency heard increases if the source moves toward the detector c Resonance occurs when the frequency of the driving force equals one of the natural vibration frequencies of the system d The pitch of a pure tone is determined by its frequency e Sound in air is a transverse wave 14 10A A SST is flying at Mach 2 twice the speed of sound About what should be the angle of its shock wave a 60o b 38o c 45o d 52o e 30o d 14 11A Two identical speakers are initially equal distances from a listener as shown at the right and the listener hears a sound maximum constructive interference When the upper speaker is moved back by a distance d 2 m the listener hears a sound minimum destructive interference About what is the longest wavelength the sound could have a 2 m b 1 m c 4 m d 0 5 m e 8 m 14 12A A string of length L 2 m with both ends fixed vibrates at a frequency of 30 Hz in its fundamental mode About what should be the speed of a wave on this string a 120 m s b 30 m s c 60 m s d 15 m s e None of these is close Phy 231 Sp 03 Homework 14 Page 2 of 4 14 13A A standing wave is shown at the right About what is its wavelength a 3 m b 4 5 m c 6 m d 7 5 m e 1 5 m 0 1 2 3 4 5 6 x m 14 14A About what is the first harmonic wavelength of a 3 0 m long half open organ pipe a 4 0 m b 1 5 m c 3 0 m d 6 0 m e 12 m 14 15A A pipe of length L 2 m is open at both ends If the speed of sound in air is about 340 m s than about what should be the first harmonic frequency of this organ pipe a 85 Hz b 128 Hz c 170 Hz d 680 Hz e 43 Hz 14 16A A violinist tunes her violin against a note struck on a piano If the frequency of the piano note is 440 Hz and she hears 2 beats sec against her violin string which one of the following frequencies could be that of her violin string a 441 Hz b 438 Hz c 440 Hz d 439 Hz e 444 Hz 14 17A Which one of the following statements is WRONG a The reference intensity for sound could be chosen so that very weak sounds would have negative sound levels in decibels b Tone quality is determined by the relative amounts of different harmonics in the sound c If two waves differing only in amplitude travel in opposite directions through a medium they cannot produce a true standing wave d When waves interfere there is a loss of total energy e Due to the Doppler effect you will hear higher pitch from a given sound source when the source is moving toward you then when the source is at rest Phy 231 Sp 03 Homework 14 Page 3 of 4 14 1B Which one of the following statements is WRONG a Both fluids and solids can transmit both longitudinal …
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