Paul Peter Urone; Roger Hinrichs

Problems

14.1 Speed of Sound, Frequency, and Wavelength

25 .

A bat produces a sound at

17,250\,\text{Hz}

and wavelength

0.019\,\text{m}

. What is the speed of the sound?

$1.7 \times 10^6\,\text{m}/\text{s}$
$8.6\times 10^5\,\text{m}/\text{s}$
$1.15\times 10^{-6}\,\text{m/s}$
$3.28\times 10^2\,\text{m}/\text{s}$

26 .

Medium	v_w (m/s)
*Gases at 0 °C*
Air	331
Carbon dioxide	259
Oxygen	316
Helium	965
Hydrogen	1290
*Liquids at 20 °C*
Ethanol	1160
Mercury	1450
Water, fresh	1480
Sea water	1540
Human tissue	1540
*Solids (longitudinal or bulk)*
Vulcanized rubber	54
Polyethylene	920
Marble	3810
Glass, Pyrex	5640
Lead	1960
Aluminum	5120
Steel	5960

Table 14.2

A sound wave with a frequency of 80 Hz is traveling through air at 0°C. The sound wave enters a block of aluminum. If the sound's frequency does not change, what happens to the sound's wavelength?

It's wavelength increases by a factor of 4.2.
It's wavelength increases by a factor of 18.
It's wavelength decreases by a factor of 4.2.
It's wavelength decreases by a factor of 18.

14.2 Sound Intensity and Sound Level

27.

Calculate the sound intensity for a sound wave traveling through air at 15° C and having a pressure amplitude of 0.80 Pa. (Hint—Speed of sound in air at 15° C is 340 m/s .)

9.6×10⁻³ W / m²
7.7×10⁻³ W / m²
9.6×10⁻⁴ W / m²
7.7×10⁻⁴ W / m²

28 .

The sound level in dB of a sound traveling through air at

0^{\circ}\text{C}

is

97\,\text{dB}

. Calculate its pressure amplitude.

$4.3\,\text{Pa}$
$0.20\,\text{Pa}$
$0.04\,\text{Pa}$
$2.1\,\text{Pa}$

14.3 Doppler Effect and Sonic Booms

29 .

An ambulance is moving away from you. You are standing still and you hear its siren at a frequency of 101 Hz. You know that the actual frequency of the siren is 105 Hz. Assuming the speed of sound is 331 m/s, what is the speed of the ambulance?

$17.07\,\text{m}/\text{s}$
$16.55\,\text{m}/\text{s}$
$14.59\,\text{m}/\text{s}$
$13.1\,\text{m/s}$

30 .

An ambulance passes you at a speed of 15.0m/s and its siren has a frequency of 995 Hz. Assuming the speed of sound in air is 331m/s, what is difference in the frequencies you perceive before and after it passes you?

$47.0\,\text{Hz}$
$43.0\,\text{Hz}$
$94.9\,\text{Hz}$
$90.0\,\text{Hz}$

14.4 Sound Interference and Resonance

31 .

What is the length of an open-pipe resonator with a fundamental frequency of

400.0\,\text{Hz}

? (Assume the speed of sound is

331\,\text{m/s}

.)

$165.1\,\text{cm}$
$82.22\,\text{cm}$
$20.25\,\text{cm}$
$41.38\,\text{cm}$

32 .

An open-pipe resonator has a fundamental frequency of

250\,\text{Hz}

. By how much would its length have to be changed to get a fundamental frequency of

300.0\,\text{Hz}

? (Assume the speed of sound is

331\,\text{m/s}

.)

$77.32\,\text{cm}$
$44.09\,\text{cm}$
$32.16\,\text{cm}$
$11.03\,\text{cm}$