Question 1

A source travelling to the right at a speed of 5 m/s emits a sound wave which is reflected off a reflector travelling to the left at a speed of 5 m/s.If the frequency of the reflected sound wave detected by a listener back at the source is 100 Hz,what is the frequency of the wave emitted at the source?

Accepted Answer

When the sound source is moving towards the reflector, the relative velocity of the wave is the difference of the velocity of sound and the velocity of the source. When the sound is reflected from the reflector, the wave is moving away from the reflector with relative velocity as the sum of the velocity of sound and the velocity of the reflector. Let the frequency of the wave emitted at the source be f. Then, the frequency of the wave detected by the listener back at the source can be calculated as follows:

f' = f(V + Vr)/(V - Vs)

Where 
f' = frequency of the reflected wave detected by the listener
V = velocity of sound
Vs = velocity of the source = 5 m/s (rightwards)
Vr = velocity of the reflector = -5 m/s (leftwards)

Substitute the values to get,

100 = f(340 - 5)/ (340 + 5)

f = 94.3 Hz

Hence, the answer is D)94.3 Hz.

Question 2

A source travelling to the right at a speed of 10 m/s emits a sound wave at a frequency of 100 Hz.The sound wave is reflected off a reflector which is travelling to the left at a speed of 5 m/s.What is the frequency of the reflected sound wave detected by a listener back at the source?

Accepted Answer

The formula for calculating the frequency of a reflected sound wave is:

f' = (v - VR) / (v + VS) * f

Where:
f' = frequency of the reflected wave
f = frequency of the original wave
v = speed of sound in air
VR = velocity of the reflector (negative since it is moving to the left)
VS = velocity of the source (positive since it is moving to the right)

Plugging in the given values:

f' = (343 - (-5)) / (343 + 10) * 100
f' = 348 / 353 * 100
f' = 98.6 Hz

Therefore, the frequency of the reflected sound wave detected by the listener back at the source is approximately 109 Hz (rounded to the nearest whole number). The closest answer choice is C.

Question 3

At a distance of 20 m from a sound source the intensity level is 60 dB.What is the intensity level (in dB)at a point 2.0 m from the source? Assume that the source radiates equally in all directions.

Accepted Answer

Intensity level is proportional to the inverse square of the distance from the source. So, if the distance is reduced to 1/10, the intensity level increases by a factor of (10)^2 = 100. Therefore, the intensity level at 2.0 m from the source is 60 + 40 (log 20/2) = 80 dB.

Question 4

Standing on the sidewalk we listen to the sound of the horn of a passing car.As the car passes us,the frequency of the sound changes from high to low in a continuous manner,that is,there is no abrupt change in the frequency heard.This is because

Accepted Answer

The observed change in frequency from high to low as the car passes is due to the Doppler effect, which occurs because the relative position of the observer to the source of sound (the car) changes, not because the pitch or intensity of the sound inherently changes. Being off to the side (not in the direct path) of the car's movement is the relevant factor here; the pitch and intensity of the horn itself do not change.

Question 5

On a hot day the temperature reaches 40.0 degree Celsius.A car,traveling 20.0 m/s,honks his horn (f = 400.0Hz).What frequency does a stationary pedestrian hear if the car is moving away from him.

Accepted Answer

The answer of On a hot day the temperature reaches...

Question 6

While enjoyable,rock concerts can be damaging to one's hearing.If you are sitting in the front row of a rock concert 5 m from the speaker system,and the sound intensity is 120 dB,how far back would you have to be such that the sound intensity drops below the recommended safe level of 90 dB?

Accepted Answer

The sound intensity level decreases by 6 dB each time the distance from the source is doubled. To decrease from 120 dB to 90 dB, a reduction of 30 dB is needed, which requires doubling the distance 5 times (2^5 = 32). Starting at 5 m, the distance becomes 5 m * 32 = 160 m.

Question 7

A source travelling to the right at a speed of 5 m/s emits a sound wave which is reflected off a reflector travelling to the left at a speed of 5 m/s.If the frequency of the reflected sound wave detected by a listener back at the source is 100 Hz,what is the frequency of the wave emitted at the source?

Accepted Answer

The answer of A source travelling to the right at...

Question 8

A driver approaches a stationary 440 Hz siren at 25 m/s.What is the frequency heard by the driver?

Accepted Answer

The frequency heard by the driver increases due to the Doppler effect, which is calculated using the formula $f' = f \frac{v + v_d}{v}$, where $f'$ is the observed frequency, $f$ is the source frequency, $v$ is the speed of sound in air (approximately 343 m/s), and $v_d$ is the speed of the driver. Substituting the given values, $f' = 440 \frac{343 + 25}{343}$, which calculates to approximately 472 Hz.

Question 9

A source travelling to the right at a speed of 10 m/s emits a sound wave at a frequency of 100 Hz.The sound wave is reflected off a reflector which is travelling to the left at a speed of 5 m/s.What is the frequency of the reflected sound wave detected by a listener back at the source?

Accepted Answer

The answer of A source travelling to the right at...

Question 10

A police car is approaching you,traveling eastward at a speed of 31.0 m/s sounds his siren (frequency of 1050 Hz).What is your velocity if you hear a frequency of 1090 Hz.The speed of sound is 344 m/s.

Accepted Answer

When a siren emitting a certain frequency approaches a stationary observer, the frequency heard by the observer is higher than the emitted frequency. When the siren moves away from the observer, the frequency heard is lower than the emitted frequency. The difference between the emitted frequency (f) and the observed frequency (f') is given by the formula:
Δf/f = (v_o ± v_s) /v_s
where vo is the velocity of the observer, vs is the velocity of the sound, and the ± sign depends on the direction of the motion (approaching or receding). 
In this case, we have:
f' = 1090 Hz, f = 1050 Hz, vs = 344 m/s, and vs = 31.0 m/s.
Plugging in the numbers and solving for the observer's velocity, we get:
vo = -19 m/s (negative sign means the observer is moving to the west).
Therefore, the correct answer is B: 19 m/s west.

Question 11

A bat flying in complete darkness emits high frequency sound of 100 kHz to locate objects.The sound travels with a speed of 340 m/s in air.The wavelength of the sound produced by the bat is

Accepted Answer

The formula for wavelength is given as:

wavelength = speed of sound / frequency

Substituting the given values, we get:

wavelength = 340 m/s / (100,000 Hz)

wavelength = 0.0034 m = 3.4 mm (since 1 m = 1000 mm)

Therefore, the wavelength of the sound produced by the bat is 3.4 mm, which is option D.

Question 12

The intensity level of the sound produced by loud rock music is 120 dB.The power incident on an eardrum of area 0.4 cm² from this sound level is

Accepted Answer

We can use the formula for sound intensity:
I = P/A

Where I is the sound intensity, P is the power, and A is the area.

We are given the sound intensity (I) as 120 dB. We can convert this to watts per square meter (W/m^2) using the formula:

I = 10log(I/I0)

Where I0 is the threshold of hearing, which is 1e-12 W/m^2.

I = 10log(120/1e-12) = 10^6 W/m^2

Now we can find the power (P) incident on the eardrum using the formula:

P = I*A

We are given the area (A) as 0.4 cm^2, which we need to convert to square meters:

A = 0.4 cm^2 * (1 m/100 cm)^2 = 4e-6 m^2

P = (10^6 W/m^2)(4e-6 m^2) = 4e-5 W = 4*10^-5 W = 4*10^-8 kW

Therefore, the answer is C, 4*10^-5 W (or 4*10^-8 kW).

Question 13

A police car siren emits a high frequency tone with a beat frequency of 10 Hz.What happens to the sound as heard by a stationary observer as the car approaches the observer?

Accepted Answer

The answer of A police car siren emits a high...

Question 14

You are a fireworks-launcher,and launch a fireworks shell into the air directly above you with an initial speed of 227 m/s.If it explodes at the top of its trajectory,how long after launch do you hear the explosion? Assume 343 m/s for the speed of sound.

Accepted Answer

The answer of You are a fireworks-launcher,and launch a fireworks...

Question 15

While standing at the roadside waiting for your ride you hear a frequency of 540 Hz from the siren of an approaching ambulance.After the ambulance passes,the observed frequency of the siren drops to 450 Hz.Take the speed of sound in air 340 m/s.The speed of the ambulance is

Accepted Answer

The answer of While standing at the roadside waiting for...

Question 16

Two identical closed-open pipes each have a fundamental frequency of 500 Hz.If the length of one of the pipes is increased by 1% What is the beat frequency when they are sounded simultaneously?

Accepted Answer

The fundamental frequency $f$ of a closed-open pipe is inversely proportional to its length $L$, i.e., $f \propto \frac{1}{L}$. If the length of one pipe is increased by 1%, its new length becomes $1.01L$, and its new frequency $f'$ becomes $f' \propto \frac{1}{1.01L}$. This means the new frequency is $f' = \frac{f}{1.01}$. Given $f = 500$ Hz, $f' = \frac{500}{1.01} \approx 495.05$ Hz. The beat frequency is the absolute difference between the two frequencies, which is $500 - 495.05 = 4.95$ Hz, which rounds to approximately 5 Hz.

Question 17

An open organ pipe has two adjacent natural frequencies of 500 and 600 Hz.Assume the speed of sound in air 340 m/s.The length of the organ pipe is

Accepted Answer

The answer of An open organ pipe has two adjacent...

Question 18

Two identical closed-open pipes each have a fundamental frequency of 500 Hz.What percent change in the length of one of the tubes will cause a beat frequency of 10 Hz when they are sounded simultaneously?

Accepted Answer

The beat frequency is given by the absolute difference in the frequencies of the two sources. Here, the beat frequency is 10 Hz, which means the frequency of one of the pipes must change to either 490 Hz or 510 Hz to achieve this difference. The fundamental frequency $f$ of a closed-open pipe is given by $f = \frac{v}{4L}$, where $v$ is the speed of sound and $L$ is the length of the pipe. Since the speed of sound $v$ remains constant, any change in frequency is inversely proportional to the change in length. To achieve a frequency of 510 Hz (a 2% increase from 500 Hz), the length of the pipe must decrease by 2% (since frequency and length are inversely related). Similarly, to achieve a frequency of 490 Hz (a 2% decrease), the length must increase by approximately 2%. Therefore, a 2% change in length is required to produce a 10 Hz beat frequency.

Question 19

Find the resonant frequency of the ear canal.Treat it as a half-open tube of diameter 8 mm and length 27 cm.Assume the temperature inside the ear canal is body temperature (37S1U1P1$\circ$S1S1P0C).

Accepted Answer

The resonant frequency of the half-open tube can be calculated using the formula:
f = (n*c)/(2*L)
where n is an integer (1, 2, 3...), c is the speed of sound, and L is the length of the tube.
Using the values given, we have:
c = 331.5 + 0.6*T = 331.5 + 0.6*37 = 353.7 m/s (at body temperature)
L = 0.27 m
n = 1 (since we are looking for the fundamental frequency)
Plugging in these values, we get:
f = (1*353.7)/(2*0.27) = 327 Hz
Therefore, the resonant frequency of the ear canal is approximately 327 Hz. The correct choice is B.

Question 20

If you need to build an organ whose fundamental frequencies cover the frequency range of a piano,from A1 (55 Hz)to C7 (3951 Hz),what is the smallest range of pipe lengths that you need to use? The speed of sound is 343 m/s.

Accepted Answer

The answer of If you need to build an organ...

Quiz 16: Sound

A source travelling to the right at a speed of 10 m/s emits a sound wave at a frequency of 100 Hz.The sound wave is reflected off a reflector which is travelling to the left at a speed of 5 m/s.What is the frequency of the reflected sound wave detected by a listener back at the source?

At a distance of 20 m from a sound source the intensity level is 60 dB.What is the intensity level (in dB) at a point 2.0 m from the source? Assume that the source radiates equally in all directions.

Standing on the sidewalk we listen to the sound of the horn of a passing car.As the car passes us,the frequency of the sound changes from high to low in a continuous manner,that is,there is no abrupt change in the frequency heard.This is because

On a hot day the temperature reaches 40.0 degree Celsius.A car,traveling 20.0 m/s,honks his horn (f = 400.0Hz) .What frequency does a stationary pedestrian hear if the car is moving away from him.

While enjoyable,rock concerts can be damaging to one's hearing.If you are sitting in the front row of a rock concert 5 m from the speaker system,and the sound intensity is 120 dB,how far back would you have to be such that the sound intensity drops below the recommended safe level of 90 dB?

A driver approaches a stationary 440 Hz siren at 25 m/s.What is the frequency heard by the driver?

A source travelling to the right at a speed of 10 m/s emits a sound wave at a frequency of 100 Hz.The sound wave is reflected off a reflector which is travelling to the left at a speed of 5 m/s.What is the frequency of the reflected sound wave detected by a listener back at the source?

A police car is approaching you,traveling eastward at a speed of 31.0 m/s sounds his siren (frequency of 1050 Hz) .What is your velocity if you hear a frequency of 1090 Hz.The speed of sound is 344 m/s.

A bat flying in complete darkness emits high frequency sound of 100 kHz to locate objects.The sound travels with a speed of 340 m/s in air.The wavelength of the sound produced by the bat is

The intensity level of the sound produced by loud rock music is 120 dB.The power incident on an eardrum of area 0.4 cm² from this sound level is

A police car siren emits a high frequency tone with a beat frequency of 10 Hz.What happens to the sound as heard by a stationary observer as the car approaches the observer?

You are a fireworks-launcher,and launch a fireworks shell into the air directly above you with an initial speed of 227 m/s.If it explodes at the top of its trajectory,how long after launch do you hear the explosion? Assume 343 m/s for the speed of sound.

While standing at the roadside waiting for your ride you hear a frequency of 540 Hz from the siren of an approaching ambulance.After the ambulance passes,the observed frequency of the siren drops to 450 Hz.Take the speed of sound in air 340 m/s.The speed of the ambulance is

Two identical closed-open pipes each have a fundamental frequency of 500 Hz.If the length of one of the pipes is increased by 1% What is the beat frequency when they are sounded simultaneously?

An open organ pipe has two adjacent natural frequencies of 500 and 600 Hz.Assume the speed of sound in air 340 m/s.The length of the organ pipe is

Two identical closed-open pipes each have a fundamental frequency of 500 Hz.What percent change in the length of one of the tubes will cause a beat frequency of 10 Hz when they are sounded simultaneously?

Find the resonant frequency of the ear canal.Treat it as a half-open tube of diameter 8 mm and length 27 cm.Assume the temperature inside the ear canal is body temperature (37^$\circ$C) .

If you need to build an organ whose fundamental frequencies cover the frequency range of a piano,from A1 (55 Hz) to C7 (3951 Hz) ,what is the smallest range of pipe lengths that you need to use? The speed of sound is 343 m/s.

Quiz 16: Sound

A source travelling to the right at a speed of 10 m/s emits a sound wave at a frequency of 100 Hz.The sound wave is reflected off a reflector which is travelling to the left at a speed of 5 m/s.What is the frequency of the reflected sound wave detected by a listener back at the source?

At a distance of 20 m from a sound source the intensity level is 60 dB.What is the intensity level (in dB) at a point 2.0 m from the source? Assume that the source radiates equally in all directions.

Standing on the sidewalk we listen to the sound of the horn of a passing car.As the car passes us,the frequency of the sound changes from high to low in a continuous manner,that is,there is no abrupt change in the frequency heard.This is because

On a hot day the temperature reaches 40.0 degree Celsius.A car,traveling 20.0 m/s,honks his horn (f = 400.0Hz) .What frequency does a stationary pedestrian hear if the car is moving away from him.

While enjoyable,rock concerts can be damaging to one's hearing.If you are sitting in the front row of a rock concert 5 m from the speaker system,and the sound intensity is 120 dB,how far back would you have to be such that the sound intensity drops below the recommended safe level of 90 dB?

A driver approaches a stationary 440 Hz siren at 25 m/s.What is the frequency heard by the driver?

A source travelling to the right at a speed of 10 m/s emits a sound wave at a frequency of 100 Hz.The sound wave is reflected off a reflector which is travelling to the left at a speed of 5 m/s.What is the frequency of the reflected sound wave detected by a listener back at the source?

A police car is approaching you,traveling eastward at a speed of 31.0 m/s sounds his siren (frequency of 1050 Hz) .What is your velocity if you hear a frequency of 1090 Hz.The speed of sound is 344 m/s.

A bat flying in complete darkness emits high frequency sound of 100 kHz to locate objects.The sound travels with a speed of 340 m/s in air.The wavelength of the sound produced by the bat is

The intensity level of the sound produced by loud rock music is 120 dB.The power incident on an eardrum of area 0.4 cm2 from this sound level is

A police car siren emits a high frequency tone with a beat frequency of 10 Hz.What happens to the sound as heard by a stationary observer as the car approaches the observer?

You are a fireworks-launcher,and launch a fireworks shell into the air directly above you with an initial speed of 227 m/s.If it explodes at the top of its trajectory,how long after launch do you hear the explosion? Assume 343 m/s for the speed of sound.

While standing at the roadside waiting for your ride you hear a frequency of 540 Hz from the siren of an approaching ambulance.After the ambulance passes,the observed frequency of the siren drops to 450 Hz.Take the speed of sound in air 340 m/s.The speed of the ambulance is

Two identical closed-open pipes each have a fundamental frequency of 500 Hz.If the length of one of the pipes is increased by 1% What is the beat frequency when they are sounded simultaneously?

An open organ pipe has two adjacent natural frequencies of 500 and 600 Hz.Assume the speed of sound in air 340 m/s.The length of the organ pipe is

Two identical closed-open pipes each have a fundamental frequency of 500 Hz.What percent change in the length of one of the tubes will cause a beat frequency of 10 Hz when they are sounded simultaneously?

Find the resonant frequency of the ear canal.Treat it as a half-open tube of diameter 8 mm and length 27 cm.Assume the temperature inside the ear canal is body temperature (37 ∘\circ∘ C) .

If you need to build an organ whose fundamental frequencies cover the frequency range of a piano,from A1 (55 Hz) to C7 (3951 Hz) ,what is the smallest range of pipe lengths that you need to use? The speed of sound is 343 m/s.

The intensity level of the sound produced by loud rock music is 120 dB.The power incident on an eardrum of area 0.4 cm² from this sound level is

Find the resonant frequency of the ear canal.Treat it as a half-open tube of diameter 8 mm and length 27 cm.Assume the temperature inside the ear canal is body temperature (37^$\circ$C) .