Physics

# Problems

PhysicsProblems

### Problems

#### 14.1Speed 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. $1.7 \times 10^6\,\text{m}/\text{s}$
2. $8.6\times 10^5\,\text{m}/\text{s}$
3. $1.15\times 10^{-6}\,\text{m/s}$
4. $3.28\times 10^2\,\text{m}/\text{s}$
26 .
 Medium vw (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?
1. It's wavelength increases by a factor of 4.2.
2. It's wavelength increases by a factor of 18.
3. It's wavelength decreases by a factor of 4.2.
4. It's wavelength decreases by a factor of 18.

#### 14.2Sound 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 .)

1. 9.6×10−3 W / m2
2. 7.7×10−3 W / m2
3. 9.6×10−4 W / m2
4. 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.
1. $4.3\,\text{Pa}$
2. $0.20\,\text{Pa}$
3. $0.04\,\text{Pa}$
4. $2.1\,\text{Pa}$

#### 14.3Doppler 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?
1. $17.07\,\text{m}/\text{s}$
2. $16.55\,\text{m}/\text{s}$
3. $14.59\,\text{m}/\text{s}$
4. $13.1\,\text{m/s}$
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?
1. $47.0\,\text{Hz}$
2. $43.0\,\text{Hz}$
3. $94.9\,\text{Hz}$
4. $90.0\,\text{Hz}$

#### 14.4Sound 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 $331\,\text{m/s}$.)
1. $165.1\,\text{cm}$
2. $82.22\,\text{cm}$
3. $20.25\,\text{cm}$
4. $41.38\,\text{cm}$
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 $331\,\text{m/s}$.)
1. $77.32\,\text{cm}$
2. $44.09\,\text{cm}$
3. $32.16\,\text{cm}$
4. $11.03\,\text{cm}$
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