PHYS 102 – Quiz Problems
Chapter 17 : Sound Waves
Dr. M. F. Al-Kuhaili
1. (TERM 001)
A moving train is blowing a whistle at 500 Hz. An observer at rest hears the sound at 480 Hz. What is the speed of the
train, and in what direction is the train moving relative to the observer?
2. (TERM 001)
A point source emits sound waves with an average output power of 8.0 W. An observer records a sound level β of 100 dB.
What is the distance between the source and the observer?
3. (TERM 002)
A sound wave of frequency 1000 Hz is propagating through air.
(a) What is the wavelength?
(b) A tube open at both ends has this frequency as a fundamental. How long is the tube?
4. (TERM 002)
A tube closed at one end resonates at 7.00 Hz and at no lower frequency. The air in the tube has a density of 1.0 kg/m3 and
a bulk modulus of 1.33 × 103 Pa. How long is the tube?
5. (TERM 002)
Two trains are traveling toward each other with a speed of 100 m/s. One train is blowing a horn at 500 Hz. What
frequency will be heard on the other train?
6. (TERM 002)
A point source emits sound waves with a power output of 80.0W.
(a) What is the intensity at a distance of 3.00 m from the source?
(b) What is the distance at which the sound level is 40 dB?
7. (TERM 012)
A point source S, located at the origin, emits sound in all directions with a wavelength of 0.35 m. A detector at P1 records
a sound level of 100 dB.
(a) What is the frequency of the sound emitted by the source?
(b) What is the power of the source?
(c) What is the intensity of sound at P2?
(d) What is the amplitude of the air oscillations at P2?
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[Speed of sound in air = 343 m/s, density of air = 1.21 kg/m , I = 10
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W/m ]
8. (TERM 012)
A sound wave of frequency 1000 Hz propagating through air has a pressure amplitude of 10.0 Pa.
(a) What is the wavelength of this wave?
(b) What is the particle displacement amplitude?
(c) What is the maximum particle speed?
(d) A pipe, closed at one end, has this frequency as a fundamental. How long is the pipe?
9. (TERM 012)
A car moving to the right at a speed of 10.0 m/s follows a fire truck. The fire truck emits sound with frequency of 500 Hz.
The van is at rest, and a passenger in the van records a frequency of 520 Hz for the sound emitted by the fire truck.
(a) What is the speed of the fire truck?
(b) What frequency will be recorded by a passenger in the car for the sound emitted by the fire truck?
10. (TERM 021)
A point source emits sound waves isotropically in air with a frequency of 500 Hz. An observer 3.0 m from the source
measures a sound level of 80 dB.
(a) Calculate the average power output of the source.
(b) Calculate the displacement amplitude of air molecules due to this wave.
(c) Calculate the pressure amplitude of this wave.
11. (TERM 021)
An ambulance travels down a highway at a speed of 35 m/s. Its siren emits sound at a frequency of 500 Hz. What is the
frequency heard by a passenger in a car traveling at 25 m/s in the opposite direction as the car approaches the ambulance
and as the car moves away from the ambulance?
12. (TERM 022)
A vibrator is used to generate sound waves in a tube closed at one end. Two resonant frequencies are heard at 52.0 Hz and
60.0 Hz.
(a) What is the length of the tube?
(b) What is the fundamental frequency of the tube?
13. (TERM 022)
Two sound sources, separated by a distance of 2 m, are in phase and emit sound waves with a frequency of 500 Hz.
Point A is 0.3 m from S1 and point B is 1.5 m from S1.
(a) What is the phase difference between the
two sound waves at point A?
(b) What is the phase difference between the
two sound waves at point B?
(c) At which point is the sound louder, why?
14. (TERM 022)
A stationary observer records a frequency of 600 Hz from the siren of an approaching police car. After the police car
passes, the observed frequency of the siren is 480 Hz.
What is the speed of the police car?
15. (TERM 033)
A point source of sound has a power of 1.0 mW and emits sound waves at a frequency of 500 Hz.
(a) What is the intensity (I) at a distance of 3.0 m away from the source?
(b) What is the sound level (β) at that distance?
(c) What is the amplitude of the air oscillations (Sm) caused by this wave?
16. (TERM 042)
A boy on a bicycle approaches a wall as he sounds his horn at a frequency f . The sound he hears reflected back from the
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wall is at a frequency 1.05 × f . What is the speed of the bicycle? Assume the speed of sound in air is 343 m/s.
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17. (TERM 042)
A tube is closed at one end and open at the other end. The tube is cut into two pieces. After cutting, the lowest resonant
frequency is 250 Hz for the piece with the closed end, and 600 Hz for the piece that is open at both ends.
(a) What was the length of the original tube?
(b) What was the fundamental frequency of the original tube?
18. (TERM 042)
Two speakers face each other as shown in the figure below. They are separated by a distance of 5.0 m, and each speaker
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has a power output of 1.0 × 10 W/m . Point P is along the line joining the two sources at a distance of 2.0 m from
speaker A. What is the sound level (β) at point P?
19. (TERM 052)
A stationary sound source (S) emits sound waves with frequency fo. An observer is moving at a speed of 10
m/s. The observer records a frequency f1 as he approaches S and a frequency f2 as he moves away from S. The
difference between f and f is 36 Hz. What is the value of f ? Take the speed of sound in air to be 340 m/s.
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2
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20. (TERM 052)
A tube is closed at one end and open at the other end. A standing sound wave is set up in the tube with 4 antinodes. The
distance between two nodes is 12.5 cm.
(a) What is the harmonic number of this wave?
(b) What is the wavelength of sound?
(c) What is the frequency of sound?
(d) What is the length of the tube?
21. (TERM 052)
Two speakers, separated by a distance d1 = 3.00 m, are in phase and emit sound waves with a frequency of 544 Hz. A
listener is initially at point A, which is a distance d2 = 4.00 m in front of one of the speakers. Now, the listener starts to
move form point A to point B along a line parallel to the line joining the two speakers. How many maxima and minima
will he observe?
22. (TERM 061)
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A point source of sound has a power 2.00 × 10 W.
a. What is the intensity 5.00 m from the source?
b. What is the sound level at that distance?
23. (TERM 061)
An ambulance emitting sound is passing by a standing observer. As the ambulance approaches him, its frequency (as
heard by the observer) is 550 Hz. The speed of the ambulance is 16 m/s.
a. What is the frequency of the sound emitted by the ambulance?
b. What frequency will be heard by the observer as the ambulance moves away?
24. (TERM 062)
A source of sound waves has a power of 1.50 µW. A listener is at point X, which is a distance of 3.00 m from the source.
a) What is the intensity of sound at point X?
b) What is the sound level at point X?
25. (TERM 061)
Tube A, which is open at one end only, is cut into two equal pieces B and C, as shown below. The fundamental frequency
of tube B is 200 Hz.
a. What is the length of tube B?
b. What is the fundamental frequency of tube A?
c. What is the fundamental frequency of pipe C?
26. (TERM 062)
Two speakers are placed 2.00 m apart and are driven by the same amplifier, as shown in the figure below. They emit
sound with a frequency of 505 Hz. Starting at the midpoint P, a detector is moved along the line joining the two detectors
towards speaker A. How far (from the midpoint) should the detector move to observe the first minimum? The speed of
sound in air is 343 m/s.
27. (TERM 062)
A tube is open at one end and closed the other end. Two consecutive resonant frequencies of the tube were found to be
550 Hz and 650 Hz. The speed of sound in air is 343 m/s.
a. What is the length of the tube?
b. What is the fundamental frequency of the tube?
c. what is the harmonic number (n) of the 550 Hz frequency?
28. (TERM 063)
The sound intensity (I) at a distance of 4.0 m from a sound source is 72 W/m2.
What is the sound level (β) at a distance of 9.0 m from the source?
29. (TERM 063)
A tube has a length of 1.20 m.
a) What is the fundamental frequency of the tube if it is open at both ends?
b) What is the fundamental frequency of the tube if it is open at one end and closed at the other end?
29. (TERM 071)
A sound source has a power output of 1.50 × 10 mW.
(a) What is the intensity (I) of sound at a distance of 5.00 m from the source?
(b) What is the sound level (β) at that distance?
30. (TERM 071)
Two sound sources are driven by the same generator. A detector is at a distance of 29.0 m from one source, and a distance
of 25.0 m from the other source. The frequency is varied between 20 Hz and 200 Hz. At what frequencies will the
detector observe maximum intensity?
31. (TERM 071)
An ambulance is moving at a speed of 15 m/s and emits sound with a frequency of 350 Hz. A car is driving in the
opposite direction, as shown in the figure below, at a speed of 12 m/s. What frequency will be detected by the driver of
the car?
15 m/s
Ambulance
12 m/s
car