30) 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
31) 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?
32) 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
33) 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
34) 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
35) 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?
36) 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
37) 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
38) 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
39) 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
40) 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
41) 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
42) 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
43) 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
44) 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
45) 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
46) 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.
47) 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.
48) 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
49) 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
50) 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
51) 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
52) 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.
53) 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.
54) 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
55) 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
56) 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
57) 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
58) 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?
59) 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?
60) 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
61) 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
62) 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 . You
are relieved that he is in pursuit of a different driver when he continues past you, but now you
perceive the frequency as What is the speed of the police car? The speed of sound in air
is
A) 38.4 m/s
B) 30 m/s
C) 39.2 m/s
D) 40.1 m/s
E) 41.7 m/s
63) 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.
A) 1300 Hz
B) 1320 Hz
C) 1270 Hz
D) 1360 Hz
E) 1370 Hz
64) You are driving along a highway at 25 m/s when you hear the siren of an emergency vehicle
traveling at constant speed in the opposite direction on the other side of the highway. When the
vehicle is approaching you, you hear the frequency of the siren as 2380 Hz, but when it is past
you the frequency becomes 1680 Hz. What is the speed of the vehicle? The speed of sound in air
is 343 m/s.
A) 35 m/s
B) 32 m/s
C) 30 m/s
D) 41 m/s
E) 50 m/s
65) You are driving along a highway at 25.0 m/s when you hear the siren of an emergency
vehicle traveling at constant speed in the opposite direction on the other side of the highway.
When the vehicle is approaching you, you hear the frequency of the siren as 2380 Hz, but when
it is past you the frequency becomes 1680 Hz. What is the frequency of the siren? The speed of
sound in air is 343 m/s.
A) 1850 Hz
B) 2000 Hz
C) 2050 Hz
D) 2010 Hz
E) 1980 Hz
66) A whistle produces sound of frequency of 1.00 kHz. If a listener moves with a speed of 30
m/s away from the whistle, what frequency does this person hear if the sound speed is 340 m/s?
A) 912 Hz
B) 919 Hz
C) 1000 Hz
D) 1090 Hz
67) A police car has an 800-Hz siren. It is traveling at 35.0 m/s on a day when the speed of
sound through air is 340 m/s. The car approaches and passes an observer who is standing along
the roadside. What change of frequency does the observer hear?
A) 0 Hz
B) 82 HZ
C) 166 Hz
D) 249 Hz
68) What is the frequency does a stationary observer hear when a train approaches her with a
speed of 30 m/s. The frequency of the train horn is 0.600 kHz and the speed of sound is 340 m/s.
A) 551 Hz
B) 600 Hz
C) 653 Hz
D) 658 Hz
69) 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?
A) 444 Hz
B) 439 Hz
C) 364 Hz
D) 361 Hz
70) 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?
A) 444 Hz
B) 439 Hz
C) 364 Hz
D) 361 Hz
71) Sonar is used to determine the speed of an object. A 40.0-kHz signal is sent out, and a 42.0-
kHz signal is returned. If the speed of sound is 345 m/s, how fast is the object moving?
A) 6.9 m/s
B) 8.4 m/s
C) 331 m/s
D) 347 m/s
72) A bat emits a sound at a frequency of 39.0 kHz as it approaches a wall. The bat detects beats
with a frequency of 827 Hz between the sound it emits and the echo bouncing from the wall.
What is the speed of the bat if the speed of sound in air is 343 m/s?
A) 2.7 m/s
B) 3.0 m/s
C) 3.6 m/s
D) 5.4 m/s
E) 9.0 m/s
73) Two in-phase loudspeakers are some distance apart. They emit sound with a frequency of
536 Hz. A microphone is moved between the speakers along the line joining the two speakers
with a constant speed of 1.60 m/s. What beat frequency is observed? The speed of sound in air is
343 m/s.
A) 5.00 Hz
B) 6.00 Hz
C) 7.00 Hz
D) 8.00 Hz
E) 9.00 Hz
74) 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
A) 1000 Hz
B) 2000 Hz.
C) 500 Hz.
D) 1500 Hz.
E) none of the above.
75) The sound from the whistle of a truck moving at 17.0 m/s toward a cliff reflects from the
cliff and is heard by the driver of the truck. When it is parked at the side of the road, the whistle
from the truck produces sound of frequency 2.267 kHz. As observed by the driver of the truck,
what is the change in frequency the sound from the whistle due to the reflection? The speed of
sound is 343 m/s.
A) 236 Hz
B) 228 Hz
C) 207 Hz
D) 118 Hz
E) 472 Hz