Chapter 14

If the distance to the water level in the well is doubled, is the time until you hear the splash twice what it was before, more than twice, or less than twice? Explain.

Is the speed of sound likely to be faster in a soft, squishy rubber ball or a hard, rigid steel ball?

A cannon \(95 \mathrm{~m}\) away shoots a cannonball straight up in the air with an initial speed of \(44 \mathrm{~m} / \mathrm{s}\). What is the speed of the cannonball when you hear the shot?

You have three tuning forks with frequencies of \(252 \mathrm{~Hz}, 256 \mathrm{~Hz}\), and \(259 \mathrm{~Hz}\). What beat frequencies are possible with these tuning forks?

Two musicians are comparing their clarinets. The first clarinet produces a tone that is known to be \(441 \mathrm{~Hz}\). When the two clarinets are played together, they produce eight beats every \(2.00 \mathrm{~s}\). If the second clarinet produces a higher-pitched tone than the first clarinet, what is the second clarinet's frequency?

How is a sound wave produced?

Which sound has the higher pitch, a sound at \(400 \mathrm{~Hz}\) or a sound at \(600 \mathrm{~Hz}\) ?

The frequency of a sound is doubled. Does the wave speed of this sound increase, decrease, or stay the same? Explain.

The frequency of a sound is doubled. Does the wavelength of this sound increase, decrease, or stay the same? Explain.

Describe a way in which sound waves are similar to waves on a string. Describe a way in which sound waves differ from waves on a string.

Two tuning forks have frequencies of \(278 \mathrm{~Hz}\) and \(292 \mathrm{~Hz}\). What is the beat frequency if both tuning forks are sounded simultaneously?

In the four cases described below, two sounds with frequencies \(f_{1}\) and \(f_{2}\) are played simultaneously. Rank the cases in order of increasing beat frequency. Indicate ties where appropriate. $$ \begin{array}{|c|c|c|c|} \hline \text { Case A } & \text { Case B } & \text { Case C } & \text { Case D } \\ \hline f_{1}=149 \mathrm{~Hz} & f_{1}=12 \mathrm{~Hz} & f_{1}=901 \mathrm{~Hz} & f_{1}=332 \mathrm{~Hz} \\ \hline f_{2}=145 \mathrm{~Hz} & f_{2}=22 \mathrm{~Hz} & f_{2}=900 \mathrm{~Hz} & f_{2}=338 \mathrm{~Hz} \\ \hline \end{array} $$

The wavelength of the third harmonic in a bottle is \(0.22 \mathrm{~m}\). What is the length of the bottle?

If the length of a pipe is increased, does the fundamental frequency increase, decrease, or stay the same? Does your answer depend on whether the pipe is open at both ends or closed at one end? Explain.

What is the wavelength of the second harmonic in a \(2.5\)-m-long pipe that is open at both ends?

What are the conditions necessary for a standing wave in a pipe that is open at one end?

What conditions produce a standing wave in a pipe that is open at both ends?

Choice The fundamental frequency of a pipe that is open at both ends is \(200 \mathrm{~Hz}\). If you cut the pipe in half, will the fundamental frequency of each half be greater than, less than, or equal to \(200 \mathrm{~Hz}\) ? Explain.

The fundamental frequency of a pipe that is open at both ends is \(200 \mathrm{~Hz}\). If you cut the pipe in half, will the fundamental frequency of each half be greater than, less than, or equal to \(200 \mathrm{~Hz}\) ? Explain.

Four standing waves, labeled A through D, are described below. Rank the standing waves in order of increasing frequency. Indicate ties where appropriate. Wave A: first harmonic; pipe closed at one end; length \(=1 \mathrm{~m}\) Wave B: first harmonic; pipe open at both ends; length \(=1 \mathrm{~m}\) Wave C: second harmonic; pipe open at both ends; length \(=3 \mathrm{~m}\) Wave D: third harmonic; pipe closed at one end; $$ \text { length }=3 \mathrm{~m} $$

What is the wavelength of the third harmonic in a \(2.7-\mathrm{m}\)-long pipe that is closed at one end?

What is the wavelength of the third harmonic in a \(2.7\)-m-long pipe that is closed at one end?

A person with perfect pitch sits on a park bench listening to the 450 -Hz horn of a moving car. (a) If the person detects a frequency of \(470 \mathrm{~Hz}\), is the car approaching or moving away? Explain. (b) How fast is the car moving?

An emergency vehicle blowing its siren is moving away from you with a speed of \(23 \mathrm{~m} / \mathrm{s}\). The sound you hear has a frequency of \(590 \mathrm{~Hz}\). What is the frequency produced by the siren?

A person with perfect pitch sits on a park bench listening to the \(450-\mathrm{Hz}\) horn of a moving car. (a) If the person detects a frequency of \(470 \mathrm{~Hz}\), is the car approaching or moving away? Explain. (b) How fast is the car moving?

The sound you hear from a moving horn has a greater frequency than the sound produced by the horn. Is the horn moving toward you or away from you? Explain.

If you move away from a stationary source of sound, is the frequency you hear greater than, less than, or equal to the frequency produced by the source? Explain.

A northern mockingbird sings a single note with a frequency \(220 \mathrm{~Hz}\) as it flies directly toward you. Is the frequency you hear greater than, less than, or equal to \(220 \mathrm{~Hz}\) ? Explain.

A pedestrian waiting for the light to change at an intersection hears a car approaching with its horn blaring. The car's horn produces sound with a frequency of \(381 \mathrm{~Hz}\), but the pedestrian hears a frequency of \(389 \mathrm{~Hz}\). How fast is the car moving?

Which do you think produces the higher observed frequency, a 110 -Hz horn moving toward you at \(12 \mathrm{~m} / \mathrm{s}\) or a \(220-\mathrm{Hz}\) horn moving away from you with a speed of \(24 \mathrm{~m} / \mathrm{s}\) ? Verify your answer by calculating the observed frequency in each case.

If the power of a speaker is doubled and the area through which the sound is emitted is also doubled, does the intensity of the sound increase, decrease, or stay the same? Explain.

What area does a sound with an intensity of \(0.067 \mathrm{~W} / \mathrm{m}^{2}\) pass through if the power of the source is \(0.21 \mathrm{~W}\) ?

What is the power of a point source of a sound that has an intensity of \(3.2 \times 10^{-6} \mathrm{~W} / \mathrm{m}^{2}\) at a distance of \(48 \mathrm{~m}\) ?

The power of a point source of sound and the distance at which the sound is heard are given below for four different cases. Rank cases A through D in order of increasing intensity. Indicate ties where appropriate. Case A: \(P=10 \mathrm{~W}, r=1 \mathrm{~m}\) Case B: \(P=20 \mathrm{~W}, r=2 \mathrm{~m}\) Case C: \(P=50 \mathrm{~W}, r=5 \mathrm{~m}\) Case D: \(P=100 \mathrm{~W}, r=5 \mathrm{~m}\)

In a pig-calling contest a caller produces a sound with an intensity level of \(100 \mathrm{~dB}\). How many such callers would be required to reach the pain level of \(120 \mathrm{~dB}\) ?

Imagine waking up to two different alarm clocks, one \(20 \mathrm{~dB}\) louder than the other. How many times louder does the "loud" alarm sound to your ears?

Why does a sound become louder as you get closer to the source?

If you double your distance from a point source of sound, by what factor does the intensity change? Explain.

Imagine waking up to two different alarm clocks, one \(20 \mathrm{~dB}\) louder than the other. How many times louder does the "loud" alarm sound to your ears?

If you double your distance from a point source of sound, by what factor does the intensity change? Explain.

Compare and contrast regions of compression and expansion (rarefaction) in a sound wave. Do these regions transfer energy from one place to another? Explain.

A sound wave passes through an area of \(1.8 \mathrm{~m}^{2}\) with an intensity of \(4.4 \times 10^{-4} \mathrm{~W} / \mathrm{m}^{2}\). What is the power of this sound?

What is the intensity of a sound from a \(25-\mathrm{W}\) point source at a distance of \(5.1 \mathrm{~m}\) ?

What is the intensity of a sound from a 25 -W point source at a distance of \(5.1 \mathrm{~m}\) ?

A car horn blasts out sound with an intensity level of \(68 \mathrm{~dB}\). How many such car horns would be required to reach an intensity level of \(78 \mathrm{~dB}\) ?

One hundred violins combine to give an intensity level of \(76 \mathrm{~dB}\). What is the intensity level of just one violin by itself?

When guitar strings \(\mathrm{A}\) and \(\mathrm{B}\) are plucked at the same time, a beat frequency of \(4 \mathrm{~Hz}\) is heard. If string \(A\) is tightened, the beat frequency decreases to \(3 \mathrm{~Hz}\). Which of the two strings had the lower frequency initially?

When guitar strings \(A\) and \(B\) are plucked at the same time, a beat frequency of \(4 \mathrm{~Hz}\) is heard. If string \(\mathrm{A}\) is tightened, the beat frequency decreases to \(3 \mathrm{~Hz}\). Which of the two strings had the lower frequency initially?

A person in the distance is hammering a nail into a board. You see the hammer strike the nail before you hear the sound. Explain.

The wavelength of sound coming from a loudspeaker is doubled. Does the frequency of the sound waves increase, decrease, or stay the same? Explain. Does the speed of the sound waves increase, decrease, or stay the same? Explain.