Question 1

You are moving at 120 km/h toward a stationary train. The train blows its 0.400-kHz whistle. Take the speed of sound to be 340 m/s. What frequency do you hear?

Accepted Answer

A)  444 Hz 
B)  439 Hz 
C)  364 Hz 
D)  361 Hz 
A)  444 Hz 
B)  439 Hz 
C)  364 Hz 
D)  361 Hz

Question 2

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?

Accepted Answer

(a) 1.93 m

Question 3

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?

Accepted Answer

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. 
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 4

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

Accepted Answer

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

Question 5

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?

Accepted Answer

(a) 0.77 m

Question 6

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

Accepted Answer

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

Question 7

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

Accepted Answer

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. 
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 8

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.

Accepted Answer

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

Question 9

By how many decibels does the intensity level of a sound increase when you triple the intensity of a source of sound?

Accepted Answer

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

Question 10

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?

Accepted Answer

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

Question 11

A siren emitting sound of frequency 1000 Hz approaches a stationary observer at one-half the speed of sound. The observer hears a frequency of

Accepted Answer

A)  1000 Hz 
B)  2000 Hz. 
C)  500 Hz. 
D)  1500 Hz. 
E)  none of the above. 
A)  1000 Hz 
B)  2000 Hz. 
C)  500 Hz. 
D)  1500 Hz. 
E)  none of the above.

Question 12

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

Accepted Answer

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. 
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 13

You are driving along a highway at 35.0 m/s when you hear the siren of a police car approaching you from behind at constant speed and you perceive the frequency as 1310 Hz. You are relieved that he is in pursuit of a different driver when he continues past you, but now you perceive the frequency as 1240 Hz. What is the frequency of the siren in the police car? The speed of sound in air is 343 m/s.

Accepted Answer

A)  1300 Hz 
B)  1320 Hz 
C)  1270 Hz 
D)  1360 Hz 
E)  1370 Hz 
A)  1300 Hz 
B)  1320 Hz 
C)  1270 Hz 
D)  1360 Hz 
E)  1370 Hz

Question 14

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 820 ${~Hz} \text {, }$ but the frequency the man hears is 774 ${~Hz}$ 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?

Accepted Answer

a) 797 Hz

Question 15

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.)

Accepted Answer

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. 
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 16

A train is traveling away from you at 120 km/h. It blows its whistle, and you hear a tone of 0.400 kHz. Take the speed of sound to be 340 m/s. What frequency does the whistle actually produce?

Accepted Answer

A)  444 Hz 
B)  439 Hz 
C)  364 Hz 
D)  361 Hz 
A)  444 Hz 
B)  439 Hz 
C)  364 Hz 
D)  361 Hz

Question 17

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

Accepted Answer

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

Question 18

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.

Accepted Answer

Question 19

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?

Accepted Answer

A)  24.9 m/s 
B)  27.2 m/s 
C)  36.2 m/s 
D)  81.0 m/s 
E)  100 m/s 
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 20

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

Accepted Answer

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

Exam 15: Traveling Waves and Sound

You are moving at 120 km/h toward a stationary train. The train blows its 0.400-kHz whistle. Take the speed of sound to be 340 m/s. What frequency do you hear?

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?

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?

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 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?

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

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

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.

By how many decibels does the intensity level of a sound increase when you triple the intensity of a source of sound?

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 siren emitting sound of frequency 1000 Hz approaches a stationary observer at one-half the speed of sound. The observer hears a frequency of

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 train is traveling away from you at 120 km/h. It blows its whistle, and you hear a tone of 0.400 kHz. Take the speed of sound to be 340 m/s. What frequency does the whistle actually produce?

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

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.

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?

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

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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?

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.