Deck 15: Traveling Waves and Sound

Question 1

The intensity of the waves from a point source at a distance d from the source is I. At what distance from the sources is the intensity equal to 2I?

A) d/2
B) d/
C) d/4
D) d/8

Answer 1

B

Question 2

What is the frequency of the wave shown in the figure?

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

Answer 2

A

Question 3

When a certain string is under tension T, the speed of a wave in the string is v. What will be the speed of a wave in the string if the tension is increased to 2T without changing the mass or length of the string?

A) v/2
B) v/
C) v
D) 2v
E) 4v

Answer 3

C

Question 4

As you are moving very quickly toward a speaker emitting a pure tone, which characteristics of the sound get larger? (There may be more than one correct choice.)

A) frequency
B) amplitude
C) wavelength
D) period
E) loudness

Question 5

In many cartoon shows, a character runs off 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 as he falls 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 6

Seven seconds after a brilliant flash of lightning, thunder shakes the house. Approximately 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 say.

Question 7

Four waves are described by the following equations, 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 8

Why does the intensity of waves from a small source decrease with the square of the distance from the source?

A) The waves run out of energy as they travel.
B) The waves spread out as they travel.
C) The medium through which the waves travel absorbs the energy of the waves.
D) The waves slow down as they travel away from the source.
E) The frequency of the waves decreases as they get farther from the source.

Question 9

What characteristics of a sound wave are related to the "pitch" of a musical note? (There could be more than one correct choice.)

A) amplitude
B) wavelength
C) frequency
D) period

Question 10

You double your distance from a sound source that is radiating equally in all directions. What happens to the intensity of the sound? It reduces to

A) one-half its original value.
B) one-fourth its original value.
C) one-sixteenth its original value.
D) none of the above

Question 11

The intensity of the waves from a point source at a distance d from the source is I. What is the intensity at a distance 2d from the source?

A) 4I
B) 2I
C) I/2
D) I/4
E) I/

Question 12

A string of length L is under tension, and the speed of a wave in the string is v. What will be the speed of a wave in the string if the length is increased to 2L but with no change in the mass or tension?

A) v/2
B) v/
C) v
D) 2v
E) 4v

Question 13

In many cartoon shows, a character runs off 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 as he falls 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 14

Which one of the curves shown in the figure best represents the variation of wave speed v as a function of tension for transverse waves on a stretched string?

A) A
B) B
C) C
D) D
E) E

Question 15

What is the wavelength of the wave shown in the figure?

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

Question 16

Four waves are described by the following equations, 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 17

Suppose that a sound source is emitting waves uniformly in all directions. If you move to a point twice as far away from the source, the frequency of the sound will be

A) unchanged.
B) half as great.
C) one-fourth as great.
D) twice as great.

Question 18

A string of mass m is under tension, and the speed of a wave in the string is v. What will be the speed of a wave in the string if the mass of the string is increased to 2m but with no change in the length or tension?

A) v/2
B) v/
C) v
D) 2v
E) 4v

Question 19

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 point 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) 120 m/s

Question 20

Sound A has a high pitch and sound B has a low pitch. Which of the following statements about these two sounds are correct? (There could be more than one correct choice.)

A) The wavelength of A is longer than the wavelength of B.
B) The period of A is shorter than the period of B.
C) The frequency of A is greater than the frequency of B.
D) Sound B travels faster than sound B through air.
E) The amplitude of A is larger than the amplitude of B.

Question 21

A 2.31-kg rope is stretched between supports that are 10.4 m apart, and has a tension in it of 49.2 N. If one end of the rope is slightly tweaked, how long will it take for the resulting disturbance to reach the other end?

A) 0.699 s
B) 0.720 s
C) 0.664 s
D) 0.615 s

Question 22

A 15-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) 1.7 kg
B) 2.1 kg
C) 2.8 kg
D) 5.1 kg
E) 3.2 kg

Question 23

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) 0.93 Hz
B) 0.00026 Hz
C) 1.1 Hz
D) 6.8 Hz
E) 0.15 Hz

Question 24

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 25

A crane lifts a 2500-kg beam at a steady rate of 15 cm/s using a steel cable whose mass per unit length is 0.65 kg/m. What is the speed of transverse waves on this cable?

A) 230 m/s
B) 580 m/s
C) 1200 m/s
D) 1900 m/s
E) 190 m/s

Question 26

The density of aluminum is 2700 kg/m³. If transverse waves travel at in an aluminum wire of diameter what is the tension on the wire?

A) 65 N
B) 39 N
C) 52 N
D) 78 N

Question 27

A piano wire of linear mass density 0.0050 kg/m is under a tension of 1350 N. What is the wave speed in this wire?

A) 130 m/s
B) 260 m/s
C) 520 m/s
D) 1040 m/s

Question 28

The speed of sound in steel is 5000 m/s. What is the wavelength of a sound wave of frequency in steel?

A) 7.58 m
B) 2.41 m
C) 1.21 m
D) 0.829 m
E) 0.132 m

Question 29

A wave whose wavelength is 0.500 m is traveling down a 500-m long wire whose total mass is 25 kg and is under a tension of 2000 N.
(a) What is the speed of the wave on the wire?
(b) Find the frequency of this wave.

Question 30

A 90-gram wire that is 1.0 m long is under tension. When a transverse wave of frequency 890 Hz travels down the wire, its wavelength is 0.10 m and its amplitude is 6.5 mm. What is the tension in the wire?

A) 710 N
B) 820 N
C) 930 N
D) 1000 N
E) 1100 N

Question 31

If a wave has a speed of 362 m/s and a period of 4.17 ms, what is its wavelength?

A) 1510 m
B) 1.51 m
C) 86.8 m
D) 86,800 m
E) 0.0115 m

Question 32

What is the frequency of a pressure wave of wavelength 2.5 m that is traveling at 1400 m/s?

A) 178 Hz
B) 1.78 kHz
C) 560 Hz
D) 5.6 kHz

Question 33

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 34

A crane lifts a 2500-kg beam using a steel cable whose mass per unit length is 0.650 kg/m. What is the speed of transverse waves on this cable if the upward acceleration of the beam is a steady 3.00 m/s²?

A) 194 m/s
B) 578 m/s
C) 1220 m/s
D) 1880 m/s
E) 222 m/s

Question 35

A 1.1-kg uniform bar of metal is 0.40 m long and has a diameter of 2.0 cm. When someone bangs one end of this bar, a 1.5 MHz shock wave is travels along the length of the bar and reaches the other end in 0.12 ms. What is the wavelength of the shock wave in the metal?

A) 2.2 mm
B) 2.6 mm
C) 3.0 mm
D) 3.4 mm
E) 3.8 mm

Question 36

Crests of an ocean wave pass a pier every If the waves are moving at what is the wavelength of the ocean waves?

A) 56 m
B) 28 m
C) 64 m
D) 48 m

Question 37

The figure shows a "snapshot" of a wave at a given instant of time. The frequency of this wave is 120 Hz. What are the (a) amplitude, (b) wavelength, and (c) speed of this wave?

Question 38

A 10-gram wire that is 6.0 m long is under tension. When a transverse wave of frequency 280 Hz travels along the wire, its wavelength is 0.60 m,and its amplitude is 8.4 mm. How much time does it take for a crest of the transverse wave to travel the length of the wire?

A) 36 ms
B) 31 ms
C) 40 ms
D) 44 ms
E) 49 ms

Question 39

A rope with a total mass of 25.0 kg is tied to a tree on one side of a 125-m wide ravine. You are pulling on the other end of the rope with a force of 415 N. If you pluck the rope at your end, how long will it take the pulse to travel across the ravine to the tree?

Question 40

Transverse waves travel at in a string that is subjected to a tension of If the string is long, what is its mass?

A) 0.515 kg
B) 0.216 kg
C) 0.366 kg
D) 0.597 kg

Question 41

The vertical displacement y(x,t) of a horizontal string aligned along the x-axis is given by the equation y(x,t) = (6.00 mm) cos[(3.25 m^-1)x - (7.22 s^-1)t]. What are the (a) speed and (b) amplitude of this wave?

Question 42

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 43

The intensity at a distance of 6.0 m from a source that is radiating equally in all directions is 6.0 × 10^-10 W/m². What is the power emitted by the source?

A) 2.1 × 10^-8 W
B) 2.7 × 10^-7 W
C) 2.1 × 10^-6 W
D) 2.7 × 10^-5 W

Question 44

Find the speed of an ocean wave whose displacement is given by the equation where x and y are in meters and t is in seconds.

A) 2.5 m/s
B) 1.9 m/s
C) 3.5 m/s
D) 4.5 m/s

Question 45

If the intensity level by 15 identical engines in a garage is 100 dB, what is the intensity level generated by each one of these engines?

A) 67 dB
B) 13 dB
C) 44 dB
D) 88 dB

Question 46

What is the intensity level in decibels of a sound with intensity 10^-3 W/m²? The threshold of human hearing is 1.0 × 10^-12 W/m².

A) 30 dB
B) 60 dB
C) 90 dB
D) 96 dB

Question 47

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 48

What is the ratio of the intensities of two sounds with intensity levels of 70 dB and 40 dB?

A) 10:1
B) 100:1
C) 1000:1
D) 10,000:1

Question 49

What are the wavelength (in meters) and frequency (in hertz) of a wave whose displacement is given by the equation y = 0.5 sin(0.20x + 120t), where x and y are in meters and t is in seconds?

A) 10 m, 0.50 Hz
B) 5.0 m, 10 Hz
C) 19 m, 120 Hz
D) 31 m, 19 Hz
E) 0.20 m, 120 Hz

Question 50

Calculate the light intensity 1.45 m from a light bulb that radiates 100 W equally in all directions.

A) 3.78 W/m²
B) 4.36 W/m²
C) 47.6 W/m²
D) 54.7 W/m²

Question 51

The vertical displacement y(x,t) of a horizontal string aligned along the x-axis is given by the equation y(x,t) = (6.00 mm) cos[(3.25 m^-1)x - (7.22 s^-1)t]. What are the (a) wavelength and (b) period of this wave?

Question 52

A plucked guitar string produces a sound wave of frequency 0.44 kHz on a day when the speed of sound is 340 m/s.
(a) What is the wavelength of the sound wave?
(b) How much time elapses between the impacts of two adjacent compressions of the sound wave on your eardrum?

Question 53

An elephant can hear sound with a frequency of 15 Hz. What is the wavelength of this wave if the speed of sound in air is 343 m/s?

Question 54

You drop a stone down a well that is 9.5 m deep. How long is it before you hear the splash? The speed of sound in air is 343 m/s and air resistance is negligible.

A) 1.2 s
B) 1.3 s
C) 1.4 s
D) 1.5 s
E) 1.6 s

Question 55

The average intensity of sunlight impinging on Earth is measured to be about 1.4 kW/m². What is the power of sunlight emitted by the sun? (Earth-Sun distance = 1.5 × 10⁸ km, Earth radius = 6.4 × 10³ km)

A) 4.0 × 10²⁶ W
B) 3.2 × 10²² W
C) 7.2 × 10¹⁴ W
D) 7.6 × 10⁸ W

Question 56

What is the intensity of a 70-dB sound? The threshold of human hearing is 1.0 × 10^-12 W/m².

A) 10^-4 W/m²
B) 10^-5 W/m²
C) 10^-6 W/m²
D) 10^-7 W/m²

Question 57

Light from a laser forms a 1.31-mm diameter spot on a wall. If the light intensity in the spot is what is the power output of the laser? Assume that all the light emitted by the laser hits the spot.

A) 21.3 mW
B) 13.2 mW
C) 17.9 mW
D) 24.7 mW

Question 58

The intensity at a distance of 6.0 m from a source that is radiating equally in all directions is 6.0 × 10^-10 W/m². What is the intensity level in dB? The threshold of human hearing is 1.0 × 10^-12 W/m².

A) 18 dB
B) 23 dB
C) 28 dB
D) 32 dB

Question 59

Two motors in a factory are running at slightly different rates. One runs at 825.0 rpm and the other at You hear the sound intensity increase and then decrease periodically due to wave interference. How long does it take between successive instances of the sound intensity increasing?

A) 1.54 s
B) 1.43 s
C) 1.66 s
D) 1.79 s

Question 60

A wire that is 1.0 m long with a mass of 90 g is under a tension of 710 N. When a transverse wave travels on the wire, its wavelength is 0.10 m and its amplitude is 6.5 mm. What is the frequency of this wave?

A) 890 Hz
B) 920 Hz
C) 1000 Hz
D) 1200 Hz
E) 1500 Hz

Question 61

A sound of 40 decibels is

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

Question 62

As shown in the figure, a man is traveling on a bicycle along a straight road that runs parallel to and right next to some railroad tracks. While moving at 10 m/s, he hears the whistle of a train that is behind him, as shown in the figure. The frequency emitted by the train's whistle is but the frequency the man hears is The speed of sound is 340 m/s.
(a) What frequency is heard by a stationary observer located between the train and the bicycle?
(b) What is the speed of the train, and is the train traveling away from or toward the bicycle?

Question 63

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

Question 64

At a distance of 15.0 m from a sound source, the intensity level is 60.0 dB. What is the intensity level (in decibels) at a point 2.00 m from the source if the source radiates equally in all directions?

A) 55.7 dB
B) 57.5 dB
C) 75.5 dB
D) 77.5 dB

Question 65

By how many decibels does the intensity level of a sound 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 66

The sound intensity level 5.0 m from a point source is 95 dB. At what distance will it be 75 dB?

A) 25 m
B) 50 m
C) 75 m
D) 225 m

Question 67

A certain glass window reduces the intensity level of the sound from 72 dB to 47 dB. By what factor is the acoustic power reduced by this glass window?

A) 3.2 × 10^-3
B) 2.2 × 10^-2
C) 5.6 × 10^-2
D) 1.0 × 10^-1
E) 1.5 × 10^-1

Question 68

A barking dog delivers about 1.0 mW of power, which is assumed to be uniformly distributed in all directions. What is the intensity level in decibels at a distance 5.00 m from the dog? The threshold of human hearing is 1.0 × 10^-12 W/m².

A) 61 dB
B) 63 dB
C) 65 dB
D) 68 dB

Question 69

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

Question 70

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 the 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

Question 71

You double your distance from a sound source that is radiating equally in all directions. What happens to the intensity level of the sound? It drops by

A) 2 dB.
B) 3 dB.
C) 6 dB.
D) 8 dB.

Question 72

The intensity level is 65 dB at a distance 5.00 m from a barking dog. What would be a reasonable estimate for the intensity level if two identical dogs very close to each other were barking? You can ignore any interference effects.

A) 65 dB
B) 68 dB
C) 130 dB
D) 136 dB

Question 73

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. Calculate a reasonable estimate for the sound intensity that the other student measures.

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 74

By how many decibels does the intensity level of a sound 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 75

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 the air is 343 m/s.

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

Question 76

A crying baby emits sound with an intensity of 8.0 × 10^-8 W/m². Calculate a reasonable estimate for the intensity level from a set of quintuplets (five babies), all crying simultaneously at the same place? 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 77

A certain factory whistle can be heard up to a distance of 2.5 km. Assuming that the acoustic output of the whistle is uniform in all directions, how much acoustic power is emitted by the whistle? The threshold of human hearing is 1.0 × 10^-12 W/m².

A) 0.079 mW
B) 0.026 mW
C) 0.26 mW
D) 0.79 mW
E) 2.6 mW

Question 78

If the intensity level of one trombone is 70 dB, calculate a reasonable estimate for the intensity level of 76 trombones all playing simultaneously in the same place?

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

Question 79

A certain siren radiates sound uniformly in all directions. At a distance of 17 m from the siren, the intensity level is 49 db. How many watts of power does this siren put out? The threshold of human hearing is 1.0 × 10^-12 W/m².

Question 80

A certain factory whistle can be heard up to a distance of 9.8 km. Assuming that the acoustic output of the whistle is uniform in all directions, at what distance from the factory is the intensity level of the whistle sound equal to 25 dB? The threshold of human hearing is 1.0 × 10^-12 W/m².

A) 550 m
B) 660 m
C) 830 m
D) 940 m
E) 1100 m