Deck 16: Sound

Question 1

The sound level in the middle of a rave is 90.0 dB.What is the sound intensity at this location?

A)1.00 * 10^-15 W/m²
B)1.00 * 10^-9 W/m²
C)1.00 * 10^-3 W/m²
D)9.00 W/m²

Answer 1

1.00 * 10^-3 W/m²

Question 2

The speed of sound in air is 319 m/s.What is the temperature of the air?

A)-20^oC
B)0^oC
C)20^oC
D)100^oC

Answer 2

-20^oC

Question 3

A bugle can be represented by a cylindrical pipe of length L = 1.24 m.Since the ends are open,the boundary conditions force the standing wave (representing the displacement of the air molecules)that is produced in the bugle to have antinodes at the open ends of the bugle,where the air molecules move back and forth the most.The longest wavelength standing wave inside the bugle is

A)0.620 m.
B)1.24 m.
C)2.48 m.
D)3.78 m.
E)4.96 m.

Answer 3

2.48 m.

Question 4

You are traveling slightly over the speed limit when you see a police car behind you in your rear view mirror.He immediately changes lanes and passes you by.You are so nervous after the police car passes you that you pull off to the side of the road and stop.Now you hear a siren,this time from an ambulance approaching from behind.The frequency you hear its siren is 1280 Hz.Once it passes,its frequency is 1080 Hz.What is the speed of the ambulance?

A)20.04 m/s
B)25.45 m/s
C)29.07 m/s
D)31.12 m/s
E)33.69 m/s

Question 5

A car horn emits a frequency of 400 Hz.A car traveling at 30.0 m/s sounds the horn as it approaches a stationary pedestrian.What frequency does the pedestrian hear? The speed of sound in air is 343 m/s.

A)400 Hz
B)411 Hz
C)425 Hz
D)438 Hz
E)442 Hz

Question 6

You stand on the curb waiting to cross the street.Suddenly you hear the sound of a horn from a car approaching you with a constant speed.You hear a frequency of 90 Hz.After the car passes you by,you hear a frequency of 75 Hz.What speed was the car traveling?

A)7.0 m/s
B)11 m/s
C)25 m/s
D)31 m/s
E)33 m/s

Question 7

You stand on the curb waiting to cross the street.Suddenly you hear the sound of a horn from a car approaching you with a constant speed of 25.0 m/s.You hear a frequency of 100 Hz.After the car passes you by,what is the frequency that you will hear?

A)86.4 Hz
B)91.0 Hz
C)109 Hz
D)115 Hz
E)120 Hz

Question 8

A standing wave in a column of air with both ends open has a frequency of 600 Hz.The next higher harmonic has a frequency of 800 Hz.What is the fundamental frequency?

A)100 Hz
B)132 Hz
C)200 Hz
D)215 Hz
E)285 Hz

Question 9

You drop a stone down a well.After 2.45 s you hear the splash.How deep is the well? The speed of sound in air is 343 m/s.

A)9.50 m
B)12.8 m
C)18.2 m
D)21.3 m
E)27.5 m

Question 10

The sound level when one student is talking during lecture is 40.0 dB.What would be the sound level if all 256 students talk at the same time during lecture? Assume each student talks equally loudly.

A)42.4 dB
B)64.1 dB
C)65.6 dB
D)296 dB

Question 11

You are sitting near the back of a twin-engine commercial jet airliner,which has the engines mounted on the fuselage near the tail.The nominal rotation speed for the turbofan in each engine is 5200 revolutions per minute,which is also the frequency of the dominant sound emitted by the engine.If one engine is running at 5214 revolutions per minute and the other at 5385 revolutions per minute,the passengers hear a pulsing noise that repeats every

A)5.8 * 10^-3 s
B)0.35 s
C)0.70 s
D)0.18 s
E)0.025 s

Question 12

Two adjacent frequencies of longitudinal standing waves in a half-open pipe are 1500 Hz and 1620 Hz.What is the fundamental frequency of the longitudinal standing waves in this half-open pipe?

A)60 Hz
B)120 Hz
C)180 Hz
D)240 Hz

Question 13

A standing wave in a column of air with both ends open has a frequency of 520 Hz.The next higher harmonic has a frequency of 780 Hz.How long is the column of air?

A)33.8 cm
B)45.1 cm
C)66.0 cm
D)86.8 cm
E)92.3 cm

Question 14

Two people are talking at a distance of 2.0 m from where you are and you measure the sound intensity as 1.5 * 10^-7 W/m².Another student is 8.0 m away from the talkers.What sound intensity does the other student measure?

A)9.4 * 10^-9 W/m²
B)1.7 * 10^-11 W/m²
C)4.7 * 10^-7 W/m²
D)6.2 * 10^-8 W/m²
E)3.5 * 10^-10 W/m²

Question 15

You drop a stone down a well that is 15.0 m deep.How long after releasing the stone do you hear the splash? The speed of sound in air is 343 m/s.

A)2.05 s
B)1.96 s
C)1.82 s
D)1.79 s
E)1.63 s

Question 16

A car traveling at 22 m/s honks its horn as it directly approaches the side of a large building.The car horn plays a long sustained note with frequency f₀ = 230 Hz (in the car's frame of reference).The sound is strongly reflected off the building back to the driver.What is the frequency of the reflected wave that the driver hears?

A)230 Hz
B)216 Hz
C)276 Hz
D)262 Hz
E)246 Hz

Question 17

What is the sound intensity 2.65 m away from a 125 W speaker that is emitting sound uniformly in all directions?

A)86.5 dB
B)1.8 dB
C)122 dB
D)128 dB
E)136 dB

Question 18

One speaker is located at the origin and the other is located at (x,y)= (0,3.00 m).The speakers emit identical sound waves of wavelength 2.00 m which are initially in phase.Where does constructive interference occur?

A)x = 1.00 m
B)x = 1.25 m
C)x = 1.50 m
D)x = 2.00 m

Question 19

The sound of 40 decibels is

A)twice as intense as the sound of 20 decibels.
B)four times as intense as the sound of 20 decibels.
C)10 times as intense as the sound of 20 decibels.
D)100 times as intense as the sound of 20 decibels.
E)1000 times as intense as the sound of 20 decibels.

Question 20

What is the speed of sound in air if its temperature is -10^oC?

A)319 m/s
B)337 m/s
C)325 m/s
D)331 m/s

Question 21

A source travelling to the right at a speed of 5 m/s emits a sound wave which is reflected off a reflector travelling to the left at a speed of 5 m/s.If the frequency of the reflected sound wave detected by a listener back at the source is 100 Hz,what is the frequency of the wave emitted at the source?

A)100 Hz
B)106 Hz
C)103 Hz
D)94.3 Hz
E)97.1 Hz

Question 22

A source travelling to the right at a speed of 10 m/s emits a sound wave at a frequency of 100 Hz.The sound wave is reflected off a reflector which is travelling to the left at a speed of 5 m/s.What is the frequency of the reflected sound wave detected by a listener back at the source?

A)105 Hz
B)104 Hz
C)109 Hz
D)96 Hz
E)91 Hz

Question 23

At a distance of 20 m from a sound source the intensity level is 60 dB.What is the intensity level (in dB)at a point 2.0 m from the source? Assume that the source radiates equally in all directions.

A)80 dB
B)45 dB
C)62 dB
D)87 dB
E)95 dB

Question 24

Standing on the sidewalk we listen to the sound of the horn of a passing car.As the car passes us,the frequency of the sound changes from high to low in a continuous manner,that is,there is no abrupt change in the frequency heard.This is because

A)the pitch of the sound of horn changes continuously.
B)the intensity of the sound heard changes continuously.
C)we are not standing directly in the path of the traveling car.
D)All of the reasons contribute to the heard effect.

Question 25

On a hot day the temperature reaches 40.0 degree Celsius.A car,traveling 20.0 m/s,honks his horn (f = 400.0Hz).What frequency does a stationary pedestrian hear if the car is moving away from him.

A)377 Hz
B)379 Hz
C)400 Hz
D)423 Hz
E)424 Hz

Question 26

While enjoyable,rock concerts can be damaging to one's hearing.If you are sitting in the front row of a rock concert 5 m from the speaker system,and the sound intensity is 120 dB,how far back would you have to be such that the sound intensity drops below the recommended safe level of 90 dB?

A)7 m
B)9 m
C)90 m
D)100 m
E)160 m

Question 27

A source travelling to the right at a speed of 5 m/s emits a sound wave which is reflected off a reflector travelling to the left at a speed of 5 m/s.If the frequency of the reflected sound wave detected by a listener back at the source is 100 Hz,what is the frequency of the wave emitted at the source?

A)100 Hz
B)106 Hz
C)103 Hz
D)94.3 Hz
E)97.1 Hz

Question 28

A driver approaches a stationary 440 Hz siren at 25 m/s.What is the frequency heard by the driver?

A)472 Hz
B)440 Hz
C)408 Hz
D)412 Hz
E)431 Hz

Question 29

A source travelling to the right at a speed of 10 m/s emits a sound wave at a frequency of 100 Hz.The sound wave is reflected off a reflector which is travelling to the left at a speed of 5 m/s.What is the frequency of the reflected sound wave detected by a listener back at the source?

A)105 Hz
B)104 Hz
C)109 Hz
D)96 Hz
E)91 Hz

Question 30

A police car is approaching you,traveling eastward at a speed of 31.0 m/s sounds his siren (frequency of 1050 Hz).What is your velocity if you hear a frequency of 1090 Hz.The speed of sound is 344 m/s.

A)19 m/s east
B)19 m/s west
C)45 m/s east
D)45 m/s west
E)You are at rest.

Question 31

A bat flying in complete darkness emits high frequency sound of 100 kHz to locate objects.The sound travels with a speed of 340 m/s in air.The wavelength of the sound produced by the bat is

A)3.4 m.
B)20.5 cm.
C)10.2 mm.
D)3.4 mm.
E)1.8 mm.

Question 32

The intensity level of the sound produced by loud rock music is 120 dB.The power incident on an eardrum of area 0.4 cm² from this sound level is

A)4 * 10^-6 W.
B)1 * 10^-5 W.
C)4 * 10^-5 W.
D)8 mW.
E)2 mW.

Question 33

A police car siren emits a high frequency tone with a beat frequency of 10 Hz.What happens to the sound as heard by a stationary observer as the car approaches the observer?

A)The siren tone increases in frequency while the beat frequency decreases.
B)The siren tone decreases in frequency while the beat frequency increases.
C)Both the siren tone and the beat frequency increase.
D)Both the siren tone and the beat frequency decrease.
E)The siren tone increases while the beat frequency remains unchanged.

Question 34

You are a fireworks-launcher,and launch a fireworks shell into the air directly above you with an initial speed of 227 m/s.If it explodes at the top of its trajectory,how long after launch do you hear the explosion? Assume 343 m/s for the speed of sound.

A)23.1 s
B)30.8 s
C)38.6 s
D)46.1 s
E)None are correct.

Question 35

While standing at the roadside waiting for your ride you hear a frequency of 540 Hz from the siren of an approaching ambulance.After the ambulance passes,the observed frequency of the siren drops to 450 Hz.Take the speed of sound in air 340 m/s.The speed of the ambulance is

A)62 m/s.
B)51 m/s.
C)44 m/s.
D)31 m/s.
E)19 m/s.

Question 36

Two identical closed-open pipes each have a fundamental frequency of 500 Hz.If the length of one of the pipes is increased by 1% What is the beat frequency when they are sounded simultaneously?

A)2 Hz
B)8 Hz
C)10 Hz
D)13 Hz
E)5 Hz

Question 37

An open organ pipe has two adjacent natural frequencies of 500 and 600 Hz.Assume the speed of sound in air 340 m/s.The length of the organ pipe is

A)0.11 m.
B)0.56 m.
C)0.81 m.
D)1.1 m.
E)1.7 m.

Question 38

Two identical closed-open pipes each have a fundamental frequency of 500 Hz.What percent change in the length of one of the tubes will cause a beat frequency of 10 Hz when they are sounded simultaneously?

A)1%
B)2%
C)3%
D)4%
E)5%

Question 39

Find the resonant frequency of the ear canal.Treat it as a half-open tube of diameter 8 mm and length 27 cm.Assume the temperature inside the ear canal is body temperature (37 ^$\circ$ C).

A)318 Hz
B)327 Hz
C)636 Hz
D)654 Hz
E)None are correct.

Question 40

If you need to build an organ whose fundamental frequencies cover the frequency range of a piano,from A1 (55 Hz)to C7 (3951 Hz),what is the smallest range of pipe lengths that you need to use? The speed of sound is 343 m/s.

A)1.09 cm to 156 cm
B)1.09 cm to 312 cm
C)2.17 cm to 156 cm
D)2.17 cm to 312 cm
E)4.34 cm to 312 cm

Question 41

A pipe with one end closed and the other end open has a fundamental frequency of 120 Hz.If the closed end is opened,what is the fundamental frequency of this pipe with both ends open?

A)40 Hz
B)60 Hz
C)80 Hz
D)240 Hz
E)480 Hz

Question 42

As a football player runs towards the band sitting behind the end zone,a horn player plays a note with frequency f.The frequency, $f'$ ,that the football player hears is

A)twice as high as f.
B)slightly higher than f.
C)the same as f.
D)slightly lower than f.
E)half of f.

Question 43

You are standing directly between two speakers that are separated by 30 m.The two speakers are each playing a pure tone of 256 Hz.You begin running directly towards one of the speakers and you measure a beat frequency of 6.0 Hz.How fast are you running?

A)1.4 m/s
B)4.0 m/s
C)5.0 m/s
D)8.5 m/s
E)43 m/s

Question 44

A guitarist tunes a string such that it is exactly in tune with a second string of equal linear mass density and length.Both vibrate with a fundamental frequency of 110.0Hz.He decreases the tension in one string so that he hears beats of 4.6Hz.What is the ratio of the tension of the first string to that of the second?

A)0.918
B)0.921
C)0.958
D)0.960
E)0.979

Question 45

An automobile traveling at 45 mi/h (= 20.0 m/s)blows a horn at a constant 600 Hz.What is the frequency observed by a stationary observer as the car approaches?

A)512 Hz
B)567 Hz
C)600 Hz
D)612 Hz
E)638 Hz

Question 46

Paul stands exactly halfway between two sound sources,one of which emits with twice the power of the other.What is the relative intensity factor (in dB)of the two sources at the point where Paul stands?

A)0 dB
B)1.0 dB
C)2.0 dB
D)3.0 dB
E)4.0 dB

Question 47

At a certain distance from a sound source the intensity is measured to be 80 dB.What is the intensity of the sound in W/m²?

A)10^-4
B)10⁸
C)10⁴
D)10⁸⁰
E)10^-16

Question 48

One piano is at rest,and another one approaches at 3.4 m/s.Both pianists are playing middle C (512 Hz).What beats does the pianist at rest hear as a result of the Doppler shift? (Use 340 m/s for v_sound.)

A)10
B)20
C)5
D)512
E)no beats

Question 49

An airplane approaches an airport control tower which is emitting a sound at 3000 Hz.The frequency heard in the plane is 4250 Hz.At what fraction of the speed of sound is the plane traveling?

A)0.12
B)0.24
C)0.29
D)0.36
E)0.42

Question 50

While standing on a sidewalk,you notice that you are halfway between a clock tower and a large building.When the clock bell strikes the hour,you hear an echo of the bell 0.33 s after hearing it directly from the clock tower.How far apart are the clock tower and the building?

A)57 m
B)110 m
C)170 m
D)230 m
E)1000 m

Question 51

A sound meter placed 5.0 m away from a speaker registers a sound level of 60 dB.If the volume on the speaker is turned down so that the power is reduced by a factor of 40,what will the sound meter now read?

A)1.5 dB
B)7.5 dB
C)15 dB
D)44 dB
E)56 dB

Question 52

The intensity of sound decreases by a factor of ten as it pass through a wall of uniform composition.If the wall is replace with a similar wall having the same thickness,but an absorption coefficient double that if the first wall,the intensity of the same sound will decrease by a factor of ____ as it passes through the new wall.

A)10
B)12
C)20
D)21
E)100

Question 53

The sound level of sound decreases by 10 dB as it pass through a wall of uniform composition.If the wall is replace with a similar wall having the same thickness,but an absorption coefficient double that if the first wall,the sound level of the same sound will decrease by ____ as it passes through the new wall.

A)10 dB
B)12 dB
C)20 dB
D)21 dB
E)100 dB

Question 54

You are standing directly between two speakers that are separated by 40 m.The two speakers are each playing a pure tone of 256 Hz.You begin running directly towards one of the speakers at 3.0 m/s.What beat frequency do you detect?

A)4.5 Hz
B)6.0 Hz
C)3.0 Hz
D)8.1 Hz
E)7.5 Hz

Question 55

My home is exactly 5.9 km from Spartan Stadium,where the football team has just scored another touchdown.Since the game is broadcast live,I can see the touchdown on TV,essentially without time delay.The time difference between when I see the touchdown and when I hear the roar from the stadium is 16.9 s.What is the temperature (in degrees Celsius)of the air?

A)30.2 ^$\circ$ C
B)25.2 ^$\circ$ C
C)20.2 ^$\circ$ C
D)15.2 ^$\circ$ C
E)10.2 ^$\circ$ C

Question 56

An explosion is detected 100 m away from ground-zero,where the intensity is recorded to be 10⁹ W/m².About 5 s later,the sound wave is recorded 1.5 km away from ground-zero.What will its intensity by at that distance? (We ignore absorption losses in this calculation!)

A)4.4 MW/m²
B)14.1 MW/m²
C)66.7 MW/m²
D)200 MW/m²
E)1000 MW/m²

Question 57

The speed of sound at 0 ^$\circ$ C is 331 m/s.At another temperature,the speed of sound is measured to be 343 m/s.What is this temperature?

A)-10 ^$\circ$ C
B)0 ^$\circ$ C
C)10 ^$\circ$ C
D)20 ^$\circ$ C
E)30 ^$\circ$ C

Question 58

A pianist considers two strings in the piano that are side-by-side.Their construction is identical in terms of their linear mass density and tension-only the length is different.If,when the strings are vibrating in their fundamental modes,a beat frequency of 2.0Hz is heard,and if the average frequency heard is 111Hz,what is the ratio of lengths of the higher frequency to lower frequency string?

A)1.04
B)1.02
C)1.00
D)0.98
E)0.96

Question 59

A pipe open at both ends has a fundamental frequency of 120 Hz.If one end of the pipe is then closed,what is the fundamental frequency of this pipe with one end closed?

A)40 Hz
B)60 Hz
C)80 Hz
D)240 Hz
E)480 Hz

Question 60

While standing on a sidewalk,you notice that you are halfway between a clock tower and a large building.The clock tower and the building are 170 m apart.When the clock bell strikes the hour,you hear an echo of the bell after hearing it directly from the clock tower.How long after hearing the bell from the clock tower do you hear the echo?

A)0.50 s
B)0.33 s
C)0.25 s
D)0.60 s
E)0.75 s