Question 1

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?

Accepted Answer

The intensity level in decibels (dB) can be calculated using the formula $L = 10 \log(I/I_0)$, where $I$ is the intensity of the sound and $I_0$ is the reference intensity. When the number of identical sound sources is increased, the total intensity is the sum of the individual intensities. For 15 identical engines producing a total of 100 dB, the intensity level of each engine can be found by first dividing the total intensity by 15 (since decibels are a logarithmic measure, we actually subtract 10 times the log of 15 from the total dB level). The calculation is as follows: $100 dB - 10 \log(15) = 100 dB - 11.76 dB = 88.24 dB$, which is approximately 88 dB.

Question 2

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.

Accepted Answer

Doubling the number of identical sound sources (like two barking dogs instead of one) increases the intensity level by about 3 dB. Therefore, if one dog produces a sound level of 65 dB, two dogs would produce a sound level of 65 dB + 3 dB = 68 dB.

Question 3

A music tuner uses a 554-Hz C# tuning fork to tune the frequency of a musical instrument. If the tuner hears a beat frequency of 2 Hz, what is the frequency of the instrument?

Accepted Answer

The beat frequency is the absolute difference between two frequencies. If the tuner hears a beat frequency of 2 Hz with a 554-Hz tuning fork, the instrument's frequency could be either 2 Hz more (556 Hz) or 2 Hz less (552 Hz) than the tuning fork's frequency.

Question 4

Two pure tones are sounded together and a particular beat frequency is heard. What happens to the beat frequency if the frequency of one of the tones is increased?

Accepted Answer

The beat frequency is the absolute difference between the frequencies of the two tones. If one frequency is increased, the difference could either increase or decrease depending on whether the increased frequency moves closer to or further from the other frequency.

Question 5

Two tuning forks have frequencies of 440 and 522 Hz. What is the beat frequency if both are sounding simultaneously?

Accepted Answer

The beat frequency is calculated by taking the absolute difference between the two frequencies: |440 Hz - 522 Hz| = 82 Hz.

Question 6

A sonic boom occurs only as an airplane just reaches the speed of sound in air, but not after it
increases its speed further.

Accepted Answer

A sonic boom occurs not only when an airplane reaches the speed of sound but also as it continues to fly at supersonic speeds. The boom is a continuous effect produced as long as the aircraft is flying faster than the speed of sound.

Question 7

In many cartoon shows, a character runs off a cliff, realizes his predicament, and lets out a scream. He continues to scream as he falls. If the physical situation is portrayed correctly, from the vantage
Point of an observer at the foot of the cliff, the pitch of the scream as he falls should be

Accepted Answer

This scenario is an example of the Doppler effect, where the frequency of a sound increases for an observer as the source of the sound approaches. As the character falls (approaches the observer), the pitch (frequency) of the scream would be perceived as higher and increasing.

Question 8

As a supersonic airplane increases its speed more and more, the half-angle of the conical shock wave

Accepted Answer

As a supersonic airplane increases its speed, the half-angle of the conical shock wave decreases. This is because the shock wave angle is inversely related to the Mach number (the ratio of the speed of the airplane to the speed of sound). As the speed of the airplane increases (thus increasing the Mach number), the cone becomes narrower.

Question 9

The sound intensity level 5.0 m from a point source is 95 dB. At what distance will it be 75 dB?

Accepted Answer

The sound intensity level decreases by 20 dB when the distance increases. Since sound intensity level decreases by 6 dB every time the distance is doubled, a decrease of 20 dB corresponds to doubling the distance approximately $2^{20/6} = 2^{10/3}$ times. This is approximately a factor of 10 increase in distance, so moving from 5 m to 50 m decreases the sound intensity level by 20 dB, from 95 dB to 75 dB.

Question 10

What is the ratio of the intensities of two sounds with intensity levels of 70 dB and 40 dB?

Accepted Answer

The answer of What is the ratio of the intensities...

Question 11

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

Accepted Answer

The answer of A barking dog delivers about 1.0 mW...

Question 12

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.

Accepted Answer

The intensity level in decibels (dB) can be calculated using the formula: $ \text{Level (dB)} = 10 \log_{10} \left( \frac{I}{I_0} \right) $, where $I$ is the intensity of the sound and $I_0$ is the reference intensity, which is the threshold of human hearing (1.0 × 10^-12 W/m^2 in this case). Plugging in the given values: $ \text{Level} = 10 \log_{10} \left( \frac{6.0 \times 10^{-10}}{1.0 \times 10^{-12}} \right) = 10 \log_{10} (600) \approx 28 $ dB.

Question 13

As you are moving very quickly toward a speaker emitting a pure tone, which characteristics of the sound get larger? (There may be more than one correct choice.)

Accepted Answer

When moving quickly toward a speaker, the frequency of the sound increases due to the Doppler effect, which can also make the sound appear louder, although loudness is subjective and depends on the listener's perception.

Question 14

Two strings both vibrate at exactly 819 Hz. The tension in one of them is then increased slightly. As a result, six beats per second are heard when both strings vibrate. What is the new frequency of the
String that was tightened?

Accepted Answer

The new frequency is 825 Hz. The original frequency is 819 Hz, and the beat frequency is 6 Hz. This means that the new frequency is 819 Hz + 6 Hz = 825 Hz.

Question 15

Two motors in a factory are running at slightly different rates. One runs at 825.0 rpm and the other at 786.0 rpm. 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?

Accepted Answer

The answer of Two motors in a factory are running...

Question 16

A person stands between two speakers driven by the same source. Each speaker produces a tone with a frequency of 200 Hz on a day when the speed of sound is 330 m/s. The person is 1.65 m
From one speaker and 4.95 m from the other. What type of interference does the person perceive?

Accepted Answer

The person perceives constructive interference because the path length difference between the two speakers is 3.3 m, which is an integer multiple (3 times) of the wavelength (1.65 m) of the sound (wavelength = speed of sound / frequency = 330 m/s / 200 Hz). This condition leads to constructive interference.

Question 17

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.

Accepted Answer

To solve this, we first find the time it takes for the stone to fall using the equation $d = \frac{1}{2}gt^2$, where $d$ is the depth of the well (9.5 m) and $g$ is the acceleration due to gravity (approximately $9.8 m/s^2$). Solving for $t$, we get $t = \sqrt{\frac{2d}{g}} = \sqrt{\frac{2*9.5}{9.8}} \approx 1.39$ seconds. Then, we calculate the time it takes for the sound to travel back up the well using the equation $t = \frac{d}{v}$, where $d$ is again the depth of the well and $v$ is the speed of sound (343 m/s). This gives $t = \frac{9.5}{343} \approx 0.028$ seconds. Adding these two times gives a total of approximately $1.39 + 0.028 \approx 1.418$ seconds, which rounds to 1.4 seconds.

Question 18

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?

Accepted Answer

The answer of At a distance of 15.0 m from...

Question 19

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?

Accepted Answer

The speed of sound through the ground is 6.0 km/s, so the distance traveled by the sound wave in 60 seconds is 6.0 km/s * 60 s = 360 km. The speed of sound in air is 343 m/s, so the distance traveled by the sound wave in air in 60 seconds is 343 m/s * 60 s = 20.58 km. The difference between these two distances is the distance between the explosion and the observer, which is 360 km - 20.58 km = 22 km.

Question 20

In many cartoon shows, a character runs off a cliff, realizes his predicament, and lets out a scream. He continues to scream as he falls. If the physical situation is portrayed correctly, from the vantage
Point of an observer at the top of the cliff leaning over the edge, the pitch of the scream as he falls
Should be

Accepted Answer

This phenomenon can be explained by the Doppler effect, which describes the change in frequency of a wave in relation to an observer moving relative to the source of the wave. As the character falls away from the observer, the sound waves stretch out, leading to a lower pitch that decreases as the distance between the character and the observer increases.

Quiz 2: Describing Motion: Kinematics in One Dimension

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?

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 music tuner uses a 554-Hz C# tuning fork to tune the frequency of a musical instrument. If the tuner hears a beat frequency of 2 Hz, what is the frequency of the instrument?

Two pure tones are sounded together and a particular beat frequency is heard. What happens to the beat frequency if the frequency of one of the tones is increased?

Two tuning forks have frequencies of 440 and 522 Hz. What is the beat frequency if both are sounding simultaneously?

A sonic boom occurs only as an airplane just reaches the speed of sound in air, but not after it increases its speed further.

In many cartoon shows, a character runs off a cliff, realizes his predicament, and lets out a scream. He continues to scream as he falls. If the physical situation is portrayed correctly, from the vantage Point of an observer at the foot of the cliff, the pitch of the scream as he falls should be

As a supersonic airplane increases its speed more and more, the half-angle of the conical shock wave

The sound intensity level 5.0 m from a point source is 95 dB. At what distance will it be 75 dB?

What is the ratio of the intensities of two sounds with intensity levels of 70 dB and 40 dB?

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

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.

As you are moving very quickly toward a speaker emitting a pure tone, which characteristics of the sound get larger? (There may be more than one correct choice.)

Two strings both vibrate at exactly 819 Hz. The tension in one of them is then increased slightly. As a result, six beats per second are heard when both strings vibrate. What is the new frequency of the String that was tightened?

Two motors in a factory are running at slightly different rates. One runs at 825.0 rpm and the other at 786.0 rpm. 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 person stands between two speakers driven by the same source. Each speaker produces a tone with a frequency of 200 Hz on a day when the speed of sound is 330 m/s. The person is 1.65 m From one speaker and 4.95 m from the other. What type of interference does the person perceive?

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.

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?

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?