Chapter 13 Text Assignment
pgs.507-510
#’s 29,41,44,46,47,52,53
Additional Problems:
1. At a track meet, you see the flash of the starter’s pistol. If you are 155 m from the start and
the air is at 20.0ºC, how long will it be before you hear the report of the pisto1? (0.451 s)
2. What is the intensity of the sound produced by a 50.0-W stereo system at a distance of 2.85
m from the stereo? What is the relative intensity in decibels? (0.49 W/m2, 117 dB)
3. On a day when the temperature is 25.0ºC, a child drops a stone into a well that is 75.2 m
deep. How much time passes before the child hears the stone hit the water? (4.14 s)
4. A piece of machinery in a factory produces a relative intensity of 80.0 dB. What would be
the relative intensity if the factory installed 12 more of these machines? (91 dB)
5. The frequencies of two notes in a chord produced by a guitar have a frequency ratio of 3:2.
If the tension on the first string is 285 N, what is the tension on the second (assuming all
other factors are equal). (127 N)
6. The six strings on a D’addario guitar have open (un-fretted) notes of E2, A2, D3, G3, B3, and
E4, with corresponding frequencies of 82 Hz, 110 Hz, 147 Hz, 196 Hz, 247 Hz, 330 Hz. If
the E2 string has a thickness of 0.046 inches, determine the thickness of each of the other 5
strings. (0.036, 0.026, 0.017, 0.013, and 0.011 in)
7. A sound detector is placed on a railway platform. A train, approaching the platform at a
speed of 36 km/h sounds its whistle. The detector detects 12 kHz as the most dominant
frequency in the whistle. If the train stops at the platform and sounds the whistle, what would
be the most dominant frequency detected? The speed of sound in air is 340 m/s. (11.65 kHz)
8. A bat emits a series of high frequency sound pulses as it approaches a moth. The pulses are
approximately 70.0 ms apart and each is about 3.0 ms long. How far away can the moth be
detected by the bat, so that the echo from one chirp returns before the next chirp is emitted?
Assume the speed of sound in air to be 343 m/s. (11.5 m)
Chapter 13
Review and Assess--ANSWERS
1. because air molecules vibrate in a direction parallel to the directions of wave motion
2. Diagrams should depict a sine curve that begins and ends at its lowest point and that has three crests
and two troughs.
3. Frequency is an objective measure of the rate of particle vibration; pitch is a subjective quality that
depends on the listener.
4. Dogs can hear waves at higher frequencies than humans can.
5. Infrasonic waves are below 20 Hz, audible waves are between 20 and 20,000 Hz, and ultrasonic
waves are greater than 20,000 Hz.
6. Molecules that have more motion (higher temperature) can transfer their vibrations more easily. This
is less noticeable in liquids and solids because the particles are closer together.
7. e
8. The siren’s pitch will drop.
9. because their short wavelengths can image small objects
10. frequency doubles; speed remains constant
11. Sound travels faster through the ground.
12. Notes that are played at the same time reach your ears at the same time.
13. Frequency does not change; wavelength does change.
14. the driver of the van
15. greater than 40 kHz
16. a
17. intensity is power per area; decibel level is relative intensity; volume doubles when intensity
increases by a factor of 10
18. 90 dB, 30 dB, 20 dB, 60 dB (Answers may vary slightly).
19. because the threshold of hearing depends on frequency
20. when a forced vibration is the same as the natural frequency of an object
21. Intensity decreases by a factor of 9.
22. because intensity decreases with distance and the sound has traveled from the source to a reflecting
surface and back
23. The violin’s sound intensity is 1
that of the orchestra’s; its volume is ¼ that of the orchestra’s.
100
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9 machines (for a total of 10)
The swing’s amplitude is maximized when the pushes match the swing’s natural frequency
Vibrations could set the bridge in motion if they match one of the bridge’s natural frequencies.
3.1 × 10−3 W
7.96 × 10−2 W/m2
a. 5.0 × 10−17 W b. 5.0 × 10−5 W
the lowest possible frequency; they are integral multiples of the fundamental frequency
a. 4.0 m b. 2.0 m c. 1.3 m d. 1.0 m
because a closed end is a node, while an open end is an antinode
The instruments have different harmonics present at various intensity levels.
3 Hz
yes; although the difference between adjacent frequencies is the same in either case, this difference
will equal the fundamental frequency if the pipe is open at both ends but will equal twice the
fundamental frequency if the pipe is closed at one end
to change the length of the air column, thereby changing the fundamental frequency
The first possible wavelength is 2L for the flute and 4L for the clarinet. Because the speed of sound is
the same in each, v  f   , the flute’s fundamental frequency is twice the clarinet’s.
The guitar’s body transfers the string’s vibrations to the air more rapidly, thereby increasing the
intensity of the sound.
As temperature increases, the speed of sound in air increases. Because f1 is proportional to v,
fundamental frequency likewise increases.
443 Hz; 886 Hz; 1330 Hz
a. 52 cm b. 640 Hz; 960 Hz c. 350 Hz
3.0 × 103 Hz
a. 958 Hz b. 27.0 cm, 45.0 cm
5 Hz
20 m; 2 × 10−2 m
0.20 s
a. 70.1 Hz b. 285
5.0 × 10−7 m
750 Hz
3.2 × 103 m
Lclosed = 1.5(Lopen)
1.9 × 10−2 m
a. 5.0 × 104 W b. 2.8 × 10−3 W
10 mosquitoes