Question 1

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 difference between the frequency of the tuning fork and the frequency of the instrument. Therefore, the frequency of the instrument could be either 556 Hz (554 Hz + 2 Hz) or 552 Hz (554 Hz - 2 Hz). Both options are equally likely.

Question 2

Consider a pipe of length L that is open at one end and closed at the other end.What are the wavelengths of the three lowest-pitch tones produced by this pipe?

Accepted Answer

For a pipe that is open at one end and closed at the other, the wavelengths of the tones produced correspond to the odd harmonics of the fundamental frequency. The fundamental frequency (first harmonic) has a wavelength of 4L, the third harmonic has a wavelength of 4L/3, and the fifth harmonic has a wavelength of 4L/5.

Question 3

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

When the tension in one string is increased, its frequency increases. The difference between the new frequency and the original frequency (819 Hz) is the number of beats per second heard, which is 6 beats per second. Therefore, the new frequency is 819 Hz + 6 Hz = 825 Hz.

Question 4

An organ pipe of length L that is open at one end resonates in its third harmonic with a wavelength of 2L/3.Is the other end of the pipe closed or open?

Accepted Answer

The third harmonic of an open pipe has antinodes at both ends, which means that the wavelength is equal to twice the length of the pipe (2L). However, the given wavelength is 2L/3, which is only possible if the pipe has an additional antinode at its closed end, making it an open pipe. Thus, the other end of the pipe must be open.

Question 5

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

As the character falls, the distance between them and the observer at the foot of the cliff increases. This causes the pitch of the scream to become higher due to the Doppler effect. Furthermore, as the character falls faster, the pitch will continue to increase. Therefore, the correct choice is B, higher than the original pitch and increasing as he falls.

Question 6

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 emitting a pure tone, the frequency of the sound increases due to the Doppler effect, which makes the pitch of the sound seem higher. Additionally, the sound may seem louder (increase in loudness) due to the decrease in distance between the source and the observer, leading to a higher intensity of sound waves reaching the observer.

Question 7

A tsunami,an ocean wave generated by an earthquake,propagates along the open ocean at 700 km/hr and has a wavelength of 750 km.What is the frequency of the waves in such a tsunami?

Accepted Answer

The speed of the wave can be related to its wavelength and frequency by the equation:
speed = wavelength x frequency
We are given that the speed of the tsunami wave is 700 km/hr and the wavelength is 750 km. Rearranging the equation to solve for frequency, we get:
frequency = speed / wavelength
Plugging in the values given, we get:
frequency = 700 km/hr / 750 km
frequency = 0.93 x 10^-3 Hz
This is approximately equal to 0.00026 Hz, which is option B.

Question 8

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 9

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 answer of Two pure tones are sounded together and...

Question 10

In a resonating pipe that is open at both ends,there

Accepted Answer

In a resonating pipe that is open at both ends, there are displacement antinodes at each end because the air at the ends can move freely, creating maximum displacement at these points.

Question 11

An pipe of length L that is open at both ends is resonating at its fundamental frequency.Which statement about the sound is correct?

Accepted Answer

The answer of An pipe of length L that is...

Question 12

Consider the standing wave on a guitar string and the sound wave generated by the string as a result of this vibration.What do these two waves have in common? (There may be more than one correct choice.)

Accepted Answer

Both the standing wave on the guitar string and the sound wave it generates share the same frequency because the frequency of the sound wave is determined by the vibration frequency of the string. They also have the same period since period is the inverse of frequency, and if the frequency is the same, the period must also be the same.

Question 13

The lowest tone to resonate in pipe of length L that is open at both ends is 200 Hz.Which one of the following frequencies will not resonate in the same pipe?

Accepted Answer

The resonant frequencies for an open pipe are given by fn = n v/2L, where n is the harmonic number, v is the speed of sound, and L is the length of the pipe. Substituting the given values, we can find the fundamental frequency f1 = v/2L = 200 Hz. The next harmonic is f2 = 2f1 = 400 Hz, which is one of the options given. The other harmonics can be found by multiplying the fundamental frequency by integers. Therefore, f3 = 3f1 = 600 Hz and f4 = 4f1 = 800 Hz are also resonant frequencies. However, f5 = 5f1 = 1000 Hz is not a resonant frequency, so the answer is E) 900 Hz, which is not one of the given options.

Question 14

In a resonating pipe that is open at one end and closed at the other end,there

Accepted Answer

In a resonating pipe that is open at one end and closed at the other end, there is a displacement node at the closed end because the air molecules cannot vibrate at the boundary between the pipe and the closed end. At the open end, there is a displacement antinode because the air molecules can freely move in and out of the pipe. Therefore, the best choice is D, which states that there is a displacement node at the closed end and a displacement antinode at the open end.

Question 15

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 (3.3 m / (330 m/s / 200 Hz) = 2) of the wavelength of the sound (1.65 m), indicating that the sound waves from the two speakers arrive in phase at the person's location.

Question 16

Suppose that a sound source is emitting waves uniformly in all directions.If you move to a point twice as far away from the source,the frequency of the sound will be

Accepted Answer

The frequency of a sound wave is determined by the source and does not change with distance. As the sound waves travel outwards from the source, their amplitude decreases due to spreading out over a larger area. This decrease in amplitude does not affect the frequency of the wave. Therefore, the frequency of the sound will remain unchanged when moving twice as far away from the source.

Question 17

The lowest tone to resonate in a pipe of length L that is closed at one end but open at the other end is 200 Hz.Which one of the following frequencies will not resonate in that pipe?

Accepted Answer

The answer of The lowest tone to resonate in a...

Question 18

Consider a pipe of length L that is open at both ends.What are the wavelengths of the three lowest-pitch tones produced by this pipe?

Accepted Answer

The three lowest-pitch tones produced by a pipe open at both ends correspond to the fundamental frequency and the next two harmonics. For a pipe open at both ends, the wavelengths of these tones are given by $2L$ for the fundamental frequency (first harmonic), $L$ for the second harmonic, and $2L/3$ for the third harmonic.

Question 19

A fisherman fishing from a pier observes that the float on his line bobs up and down,taking 2.4 s to move from its highest point to its lowest point.He also estimates that the distance between adjacent wave crests is 48 m.What is the speed of the waves going past the pier?

Accepted Answer

The time for one complete wave cycle is equal to the time it takes for the float to move from its highest point to its lowest point, which is 2.4 seconds. Therefore, the frequency of the waves is:

frequency = 1/time = 1/2.4 s = 0.42 Hz

The speed of the waves is equal to the product of the frequency and the wavelength:

speed = frequency x wavelength = 0.42 Hz x 48 m = 20.16 m/s

Therefore, the best choice is C) 10 m/s, since it is closest to the calculated value of 20.16 m/s when rounded to one significant figure.

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

As the character falls, they will be moving away from the observer at the top of the cliff. This means that the sound waves of their scream will be stretched out or "stretched" as they move further away, resulting in a lower pitch. Additionally, the scream will decrease in volume as the character gets farther away. Therefore, the correct option would be lower than the original pitch and decreasing as they fall.

Quiz 21: Mechanical Waves

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?