Deck 14: Waves and Sound

Question 1

Sound waves in air are transverse waves.

Answer 1

False

Question 2

Infrasound carries over long distances better than ultrasound.

Answer 2

True

Question 3

Bats use infrasound to navigate.

Answer 3

False

Question 4

A wave pulse on a string whose end is fixed is reflected without inversion.

Question 5

As the temperature of the air increases, what happens to the velocity of sound? (Assume that all other factors remain constant.)

A) It increases.
B) It decreases.
C) It does not change.
D) It increases when atmospheric pressure is high and decreases when the pressure is low.
E) It increases when atmospheric pressure is low and decreases when the pressure is high.

Question 6

The pitch of a sound is determined by

A) the amplitude.
B) the speed.
C) the frequency.
D) the wavelength.
E) none of the above

Question 7

Four waves are described by the following expressions, where distances are measured in meters and times in seconds. I y = 0.12 cos(3x - 21t)
II y = 0.15 sin(6x + 42t)
III y = 0.13 cos(6x + 21t)
IV y = -0.23 sin(3x - 42t)
Which of these waves have the same speed?

A) I and II
B) I and III
C) II and III
D) III and IV
E) II and IV

Question 8

Four waves are described by the following expressions, where distances are measured in meters and times in seconds. I y = 0.12 cos(3x - 21t)
II y = 0.15 sin(6x + 42t)
III y = 0.13 cos(6x + 21t)
IV y = -0.23 sin(3x - 42t)
Which of these waves travel in the +x direction?

A) I and II
B) I and III
C) II and IV
D) I and IV
E) II and III

Question 9

Four waves are described by the following expressions, where distances are measured in meters and times in seconds. I y = 0.12 cos(3x - 21t)
II y = 0.15 sin(6x + 42t)
III y = 0.13 cos(6x + 21t)
IV y = -0.23 sin(3x - 42t)
Which of these waves have the same period?

A) I and III, and also II and IV
B) I and IV, and also II and III
C) I and II, and also III and IV
D) All of them have the same period.
E) They all have different periods.

Question 10

Write an expression for a harmonic wave that has an amplitude of 18 cm, a wavelength of 2.0 m, and propagates to the left at 15 m/s.

Question 11

FIGURE 14-1
In Figure 14-1, the wavelength is

A) 8 m.
B) 4 m.
C) 2 m.
D) 1 m.
E) cannot be determined from the given information

Question 12

In western movies you often see a person putting his ear against the rails in the train tracks to find out if a train is approaching. Why would this give him advance knowledge of the approach of a train?

Question 13

Seven seconds after a brilliant flash of lightning, thunder shakes the house. How far was the lightning strike from the house?

A) Much closer than one kilometer
B) About one kilometer away
C) About two kilometers away
D) Much farther away than two kilometers
E) It is impossible to predict.

Question 14

FIGURE 14-1
In Figure 14-1, the frequency is

A) 0.5 Hz.
B) 1 Hz.
C) 2 Hz.
D) 4 Hz.
E) cannot be determined from the given information

Question 15

Two strings are made of the same material. String 1 has radius r₁ while string 2 has radius r₂ = r₁/2. When stretched by the same tension, the respective speed of propagation of waves v₁ and v₂ satisfy the condition

A) v₁ = v₂.
B) v₁ = 2v₂.
C) v₁ = v₂/ .
D) v₁ = v₂/2.
E) v₁ = v₂/4.

Question 16

A wave pulse traveling to the right along a thin cord reaches a discontinuity where the rope becomes thicker and heavier. What is the orientation of the reflected and transmitted pulses?

A) Both are right side up.
B) The reflected pulse returns right side up while the transmitted pulse is inverted.
C) The reflected pulse returns inverted while the transmitted pulse is right side up.
D) Both are inverted.
E) It is impossible to predict.

Question 17

Sound vibrations with frequencies less than 20 Hz are called

A) infrasonics.
B) ultrasonics.
C) supersonics.
D) infrared.
E) megasonics.

Question 18

A uniform rope hangs from a ceiling. Without tugging on the rope, you give the bottom of the rope a wiggle and a wave travels upward along the rope. What can you say about the speed of the wave as the wave travels up the rope?

Question 19

What is the audible range of sound frequencies?

Question 20

Give at least one example of each of the following:
(a) longitudinal standing wave.
(b) transverse standing wave.

Question 21

A sound source departs from a stationary observer. The frequency heard by the observer is

A) higher than the source.
B) lower than the source.
C) the same as that of the source.
D) equal to zero.
E) impossible to predict.

Question 22

By what amount does the intensity level increase when you triple the intensity of a source of sound?

A) 9.5 dB
B) 4.8 dB
C) 6.0 dB
D) 3.0 dB
E) 12 dB

Question 23

In many cartoon shows, a character runs of a cliff, realizes his predicament and lets out a scream. He continues to scream as he falls. If the physical situation is portrayed correctly, from the vantage point of an observer at the top of the cliff leaning over the edge, the pitch of the scream should be

A) higher than the original pitch and constant.
B) higher than the original pitch and increasing as he falls.
C) lower than the original pitch and constant.
D) lower than the original pitch and decreasing as he falls.
E) It is impossible to predict.

Question 24

Sound vibrations with frequencies greater than 20,000 Hz are called

A) infrasonics.
B) ultrasonics.
C) supersonics.
D) infrared.
E) megasonics.

Question 25

The wavelengths corresponding to the harmonics of a string with fixed ends can be found by saying that the length of the string must be equal to

A) an odd number of quarter-wavelengths.
B) an odd number of third-wavelengths.
C) an odd number of half-wavelengths.
D) an integer number of half-wavelengths.
E) an integer number of wavelengths.

Question 26

In a resonating pipe which is open at both ends, there

A) are displacement nodes at each end.
B) are displacement antinodes at each end.
C) is a displacement node at one end and a displacement antinode at the other end.
D) none of the above

Question 27

Two wave pulses with equal positive amplitudes pass each other on a string. One is traveling toward the right and the other toward the left. At the point that they occupy the same region of space at the same time

A) constructive interference occurs.
B) destructive interference occurs.
C) a standing wave is produced.
D) a traveling wave is produced.

Question 28

Car 1 moves toward car 2 with speed v. An observer in car 2 measures the frequency of the sound emitted by car 1's horn to be f. Now, car 1 remains stationary while car 2 moves toward car 1 with speed v. The observer in car 2 now measures the frequency of car 1's horn to be f'. The relationship between the observed frequencies is

A) f < f'.
B) f = f'.
C) f = 2 f'.
D) f = 1/2 f'.
E) f > f'.

Question 29

The reason that you do not observe a Doppler shift when you listen to the car radio while driving is that

A) the source and observer are moving at the same speed.
B) the air inside the car is moving at the same speed as the car.
C) the speed of the car is too slow compared to the speed of sound.
D) the speed of the car is too fast compared to the speed of sound.
E) there is a Doppler shift but we don't notice it.

Question 30

A sound source approaches a stationary observer. The frequency heard by the observer is

A) higher than the source.
B) lower than the source.
C) the same as that of the source.
D) equal to zero.
E) impossible to predict.

Question 31

Two cars are traveling in the same direction and with the same speed along a straight highway. Does either driver hear a different frequency from the other car's horn than they would if the cars were stationary?

A) Yes, they both experience a Doppler shift.
B) Only the driver of the front car experiences a Doppler shift.
C) Only the driver of the rear car experiences a Doppler shift.
D) No, because neither driver experiences a Doppler shift.
E) It is impossible to predict.

Question 32

By what amount does the intensity level decrease when you triple your distance from a source of sound?

A) 9.5 dB
B) 4.8 dB
C) 6.0 dB
D) 12 dB
E) 3.0 dB

Question 33

In many cartoon shows, a character runs of a cliff, realizes his predicament and lets out a scream. He continues to scream as he falls. If the physical situation is portrayed correctly, from the vantage point of an observer at the foot of the cliff, the pitch of the scream should be

A) higher than the original pitch and constant.
B) higher than the original pitch and increasing as he falls.
C) lower than the original pitch and constant.
D) lower than the original pitch and decreasing as he falls.
E) It is impossible to predict.

Question 34

Which part of a vibrating string experiences the maximum acceleration?

A) nodes
B) ends
C) antinodes

Question 35

Two wave pulses pass each other on a string. The one traveling toward the right has a positive amplitude, while the one traveling toward the left has an equal amplitude in the negative direction. At the point that they occupy the same region of space at the same time

A) constructive interference occurs.
B) destructive interference occurs.
C) a standing wave is produced.
D) a traveling wave is produced.

Question 36

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 37

An open pipe of length L is resonating at its fundamental frequency. Which statement is correct?

A) The wavelength is 2L and there is a displacement node at the pipe's midpoint.
B) The wavelength is 2L and there is a displacement antinode at the pipe's midpoint.
C) The wavelength is L and there is a displacement node at the pipe's midpoint.
D) The wavelength is L and there is a displacement antinode at the pipe's midpoint.
E) The wavelength is 3L/2 and there are two displacement antinodes located inside the pipe.

Question 38

The wavelengths corresponding to the harmonics of an organ pipe that is open at one end and closed at the other can be found by saying that the length of the pipe must be equal to

A) an odd number of quarter-wavelengths.
B) an odd number of third-wavelengths.
C) an odd number of half-wavelengths.
D) an integer number of half-wavelengths.
E) an integer number of wavelengths.

Question 39

Consider an open pipe of length L. What are the wavelengths of the three lowest tones produced by this pipe?

A) 16L, 4L, L
B) 4L, 2L, L
C) 2L, L, L/2
D) 2L, L, 2L/3
E) 4L, 4L/3, 4L/5

Question 40

Sound intensity is defined as

A) the loudness of a sound.
B) the sound energy passing through a unit of area.
C) the sound power per unit time.
D) the sound power per unit volume.
E) the sound energy passing through a unit of area per unit time.

Question 41

In a resonating pipe which is open at one end and closed at the other, there

A) are displacement nodes at each end.
B) are displacement antinodes at each end.
C) is a displacement node at the open end and a displacement antinode at the closed end.
D) is a displacement node at the closed end and a displacement antinode at the open end.

Question 42

A pipe of length L closed at one end is resonating at its fundamental frequency. Which statement is correct?

A) The wavelength is 4L and there is a displacement node at the pipe's open end.
B) The wavelength is 4L and there is a displacement antinode at the pipe's open end.
C) The wavelength is L and there is a displacement node at the pipe's open end.
D) The wavelength is L and there is a displacement antinode at the pipe's open end.

Question 43

In the open ocean, the tides are waves that have a period of 12 hours and a speed of 750 km/hr. What is their wavelength?

Question 44

Two steel wires are stretched with the same tension. The first wire has a diameter of 0.610 mm and the second wire has a diameter of 0.910 mm. If the speed of waves traveling along the first wire is 54.0 m/s, what is the speed of waves traveling along the second wire?

A) 24.9 m/s
B) 27.2 m/s
C) 36.2 m/s
D) 81.0 m/s
E) 100 m/s

Question 45

The speed of surface waves in deep water is given by v = gT/2π. What is the wavelength of a wave that has a period of 3.00 s?

A) 4.68 m
B) 29.4 m
C) 14.1 m
D) 44.1 m
E) 39.4 m

Question 46

If the intensity level of one trombone is 70 dB and that of one cornet is 65 dB, which is louder:
76 trombones or 110 cornets?

Question 47

A 6.00-m length of rope has a mass of 700 g. It is pulled taught with a force of 100 N. What is the speed of waves on the rope?

A) 29.3 m/s
B) 11.7 m/s
C) 42.0 m/s
D) 3.42 m/s
E) 4.20 m/s

Question 48

A harmonic wave has a wavelength of 2.0 m and a frequency of 5.0 Hz. What is the speed of the wave?

A) 10 m/s
B) 0.40 m/s
C) 0.50 m/s
D) 0.10 m/s
E) 2.5 m/s

Question 49

A factory siren indicating the end of a shift has a frequency of 90.0 Hz.
(a) What frequency is perceived by the occupant of a car traveling towards the factory at 25 m/s?
(b) What frequency is perceived by the occupant of a car traveling away from the factory at 30 m/s?

Question 50

A 15.0-m rope is pulled taut with a tension of 140 N. It takes 0.545 s for a wave to propagate along the rope. What is the mass of the rope?

A) 1.67 kg
B) 2.10 kg
C) 2.77 kg
D) 5.09 kg
E) 3.19 kg

Question 51

A harmonic wave travels with a speed of 200 m/s and has a wavelength of 0.800 m. What is the frequency of the wave?

A) 25.0 Hz
B) 40.0 Hz
C) 125 Hz
D) 80.0 Hz
E) 250 Hz

Question 52

In order to produce beats, the two sound waves should have

A) the same amplitude.
B) slightly different amplitudes.
C) the same period.
D) the same frequency.
E) slightly different frequencies.

Question 53

Two pure tones are sounded together and a particular beat frequency is heard. What happens to the beat frequency if the frequency of one of the tones is increased?

A) It increases.
B) It decreases.
C) It does not change.
D) It becomes zero.
E) It could either increase or decrease.

Question 54

Two in-phase loudspeakers are placed along a wall and are separated by a distance of 4.00 m. They emit sound with a frequency of 514 Hz. A person is standing away from the wall, in front of one of the loudspeakers.
(a) What is the closest distance from the wall the person can stand and hear constructive interference?
(b) What is the closest distance from the wall the person can stand and hear destructive interference?

Question 55

A tsunami, an ocean wave generated by an earthquake, propagates along the open ocean at 700 km/hr and has a wavelength of 750 km. What is the frequency of the waves in such a tsunami?

A) 0.933 Hz
B) 0.000259 Hz
C) 1.07 Hz
D) 6.76 Hz
E) 0.148 Hz

Question 56

A fisherman fishing from a pier observes that the float on his line bobs up and down, taking 2.4 s to move from its highest to its lowest point. He also estimates that the distance between adjacent wave crests is 48 m. What is the speed of the waves going past the pier?

A) 1.0 m/s
B) 20 m/s
C) 10 m/s
D) 5.0 m/s
E) 115 m/s

Question 57

An elephant can hear sound with a frequency of 15.0 Hz. What is the wavelength of this wave?
The speed of sound in air is 343 m/s.

Question 58

A ten-year exposure to the sound of a riveting machine will cause your threshold of hearing to shift from 0 dB to 30 dB. What is the sound intensity corresponding to 30 dB?
The normal lowest detectable intensity is 1.0 × 10^-12 W/m².

Question 59

What is the wave speed in a brass wire with a radius of 0.500 mm stretched with a tension of 125 N? The density of brass is 8.60 × 10³ kg/m³.

A) 0.121 m/s
B) 100 m/s
C) 136 m/s
D) 500 m/s
E) 68.8 m/s

Question 60

Consider a closed pipe of length L. What are the wavelengths of the three lowest tones produced by this pipe?

A) 16L, 4L, L
B) 4L, 2L, L
C) 2L, L, L/2
D) 2L, L, 2L/3
E) 4L, 4L/3, 4L/5

Question 61

The vertical displacement of a string is given by y(x,t) = (6.00 mm) cos[(3.25 m^-1)x - (7.22 s^-1)t]. What is the period of the wave?

A) 7.22 s
B) 1.93 s
C) 0.870 s
D) 0.308 s
E) 0.139 s

Question 62

A car horn emits a frequency of 400 Hz. A car traveling at 20.0 m/s sounds the horn as it goes away from a stationary pedestrian. What frequency does the pedestrian hear? The speed of sound in air is 343 m/s.

A) 378 Hz
B) 389 Hz
C) 411 Hz
D) 422 Hz
E) 450 Hz

Question 63

You drop a stone down a well that is 9.50 m deep. How long is it before you hear the splash? The speed of sound in air is 343 m/s.

A) 1.39 s
B) 1.40 s
C) 1.41 s
D) 1.42 s
E) 1.43 s

Question 64

An earthquake generates three kinds of waves: surface waves (L-waves), which are the slowest and weakest, shear (S) waves, which are transverse waves and carry most of the energy, and pressure (P) waves, which are longitudinal waves and are the fastest. The speed of P waves is approximately 7 km/s, and that of S waves is about 4 km/s. People do not generally feel the P waves, but animals seem to be sensitive to them. If a person reports that her dog started barking 20 seconds "before the earthquake," then approximately how far was the origin of the earthquake?

A) 100 km
B) 200 km
C) 300 km
D) 400 km
E) 500 km

Question 65

A factory siren indicating the end of a shift has a frequency of 80 Hz. What frequency is perceived by the occupant of a car traveling away from the factory at 30 m/s? The speed of sound in air is 343 m/s.

A) 73 Hz
B) 75 Hz
C) 77 Hz
D) 79 Hz
E) 81 Hz

Question 66

A factory siren indicating the end of a shift has a frequency of 80 Hz. What frequency is perceived by the occupant of a car traveling towards the factory at 30 m/s? The speed of sound in air is 343 m/s.

A) 83 Hz
B) 85 Hz
C) 87 Hz
D) 89 Hz
E) 91 Hz

Question 67

Two people are talking at a distance of 3.0 m from where you are and you measure the sound intensity as 1.1 × 10^-7 W/m². Another student is 4.0 m away from the talkers. What sound intensity does the other student measure?

A) 6.2 × 10^-8 W/m²
B) 1.5 × 10^-7 W/m²
C) 8.3 × 10^-8 W/m²
D) 7.8 × 10^-7 W/m²
E) 2.5 × 10^-8 W/m²

Question 68

The vertical displacement of a string is given by y(x,t) = (6.00 mm) cos[(3.25 m^-1)x - (7.22 s^-1)t]. What is the wavelength of the wave?

A) 3.25 m
B) 1.93 m
C) 0.870 m
D) 0.308 m
E) 0.139 m

Question 69

The vertical displacement of a string is given by y(x,t) = (6.00 mm) cos[(3.25 m^-1)x - (7.22 s^-1)t]. What is the speed of the wave?

A) 0.450 m/s
B) 1.41 m/s
C) 2.22 m/s
D) 3.16 m/s
E) 23.5 m/s

Question 70

A car horn emits a frequency of 400 Hz. A car traveling at 20.0 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) 200 Hz
B) 375 Hz
C) 400 Hz
D) 425 Hz
E) 450 Hz

Question 71

The vertical displacement of a string is given by y(x,t) = (6.00 mm) cos[(3.25 m^-1)x - (7.22 s^-1)t]. What is the amplitude of the wave?

A) 6.00 mm
B) 12.0 mm
C) 3.00 mm
D) 2.00 mm
E) None of the other choices is correct.

Question 72

The intensity level of a power mower at a distance of 1.0 m is 100 dB. You wake up one morning to find that four of your neighbors are mowing their lawn 20 m from your open bedroom window. What is the intensity level in your bedroom?

A) 80 dB
B) 104 dB
C) 400 dB
D) 50 dB
E) 40 dB

Question 73

The wave speed in an aluminum wire with a radius of 1.00 mm is 120 m/s. What is the tension in the wire? The density of aluminum is 2.70 × 10³ kg/m³.

A) 112 N
B) 100 N
C) 134 N
D) 427 N
E) 122 N

Question 74

You drop a stone down a well. You hear the splash 1.63 s later. How deep is the well? The speed of sound in air is 343 m/s.

A) 6.96 m
B) 20.2 m
C) 12.5 m
D) 18.8 m
E) 20.0 m

Question 75

If the intensity level of one trombone is 70 dB, what is the intensity level of 76 trombones?

A) 146 dB
B) 89 dB
C) 70 dB
D) 76 dB
E) 82 dB

Question 76

The speed of sound through the ground is about 6.0 km/s while the speed of sound in air is 343 m/s. A very powerful explosion occurs some distance away and you feel the ground vibrate 60 seconds before you hear the sound of the explosion. How far away is the explosion?

A) 20 km
B) 22 km
C) 25 km
D) 27 km
E) 30 km

Question 77

You are driving along a highway at 35.0 m/s when you hear the siren of a police car approaching you from behind and you perceive the frequency as 1340 Hz. You are relieved that he is in pursuit of a different speeder when he continues past you, but now you perceive the frequency as 1300 Hz. What is the speed of the police car? The speed of sound in air is 343 m/s.

A) 38.4 m/s
B) 30 m/s
C) 39.2 m/s
D) 40.1 m/s
E) 41.7 m/s

Question 78

A car approaches you at a constant speed, sounding its horn, and you hear a frequency of 76 Hz. After the car goes by, you hear a frequency of 65 Hz. What is the frequency of the sound emitted by the horn? The speed of sound in air is 343 m/s.

A) 68 Hz
B) 69 Hz
C) 70 Hz
D) 71 Hz
E) 72 Hz

Question 79

A crying baby emits sound with an intensity of 8.0 × 10^-8 W/m². What is the intensity level for a set of quintuplets? The lowest detectable intensity is 1.0 × 10^-12 W/m².

A) 79 dB
B) 69 dB
C) 56 dB
D) 49 dB
E) 36 dB

Question 80

As you stand by the side of the road, a car approaches you at a constant speed, sounding its horn, and you hear a frequency of 76 Hz. After the car goes by, you hear a frequency of 65 Hz. What is the speed of the car? The speed of sound in air is 343 m/s.

A) 26 m/s
B) 27 m/s
C) 28 m/s
D) 29 m/s
E) 30 m/s