Question 1

​An ambulance with its siren on is heading due east along a straight road at 60 mph.A car is also moving along the same road.In which case will the driver of the car perceive the frequency of the siren to be lowest?

Accepted Answer

The frequency perceived by the driver will be lowest when the relative speed between the car and the ambulance is highest in the opposite direction. In option B, the car is moving west at 65 mph while the ambulance is moving east at 60 mph, resulting in the highest relative speed away from the ambulance.

Question 2

A string of length L with fixed ends is made to go into standing wave patterns.What is the longest wavelength associated with all possible standing wave patterns in this situation?

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Question 3

If the tension on a guitar string is increased by a factor of 3,the fundamental frequency at which it vibrates is changed by what factor?

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Question 4

While standing at a crosswalk,you hear a frequency of 600 Hz from an approaching police car.After the police car passes,its frequency is 400 Hz.What is the speed of the police car? (speed of sound = 340 m/s)

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Question 5

How many nodes does a standing wave in a string have at the frequency of the sixth harmonic?

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Question 6

A 550-Hz whistle is moved toward a listener at a speed of 25.0 m/s.At the same time,the listener moves at a speed of 35.0 m/s in a direction away from the whistle.What is the apparent frequency heard by the listener? (The speed of sound is 340 m/s. )

Accepted Answer

To find the apparent frequency heard by the listener, we need to use the formula for Doppler effect:

f' = f (v + v₀)/(v - vₛ)

where 
f = frequency emitted by the whistle (550 Hz) 
v = speed of sound (340 m/s) 
v₀ = speed of the listener (35.0 m/s) 
vₛ = speed of the source (whistle) (25.0 m/s, but negative since it's moving towards the listener)

Plugging in the values, we get:

f' = 550 * (340 + 35)/(340 - (-25)) 
f' = 550 * 375/365 
f' ≈ 533 Hz

Therefore, the best choice is B, with an explanation as shown above.

Question 7

A buzzer with frequency f₀ is thrown straight upwards.On the buzzer's trip down,what is the frequency behavior heard by an observer below?

Accepted Answer

The Doppler effect causes the frequency of the sound heard by an observer to increase as the source of the sound (the buzzer) moves closer. Since the buzzer is moving downwards towards the observer, the frequency heard will be an increasing one greater than the original frequency emitted by the buzzer.

Question 8

Standing waves can result from _____ waves.

Accepted Answer

Standing waves can result from both longitudinal and transverse waves, as they are a phenomenon of wave interference that can occur with any type of wave that reflects and interferes with itself.

Question 9

When I stand halfway between two speakers,with one on my left and one on my right,a musical note from the speakers gives me constructive interference.How far to my left should I move to obtain destructive interference?

Accepted Answer

To achieve destructive interference, you need to move a quarter of a wavelength from the point of constructive interference, as this will cause the waves from the two speakers to be out of phase by half a wavelength.

Question 10

Two loudspeakers are placed side by side and driven by the same source at 525 Hz.A listener is positioned in front of the two speakers and on the line separating them,thus creating a constructive interference at the listener's ear.If one of the speakers is gradually pushed toward the listener,how far must it be moved to repeat the condition of constructive interference at the listener's ear? (The speed of sound = 340 m/s. )

Accepted Answer

The distance between the speakers must be equal to half a wavelength to create constructive interference. The wavelength of a sound wave is given by the formula:$$\lambda = v/f$$where:* $$\lambda$$ is the wavelength in meters* $$v$$ is the speed of sound in meters per second* $$f$$ is the frequency in HertzIn this case, the frequency is 525 Hz and the speed of sound is 340 m/s, so the wavelength is:$$\lambda = 340 m/s / 525 Hz = 0.65 m$$Therefore, the speakers must be moved 0.65 m closer to the listener to create constructive interference again.

Question 11

A sound source of frequency 1 100 Hz moves at 40.0 m/s toward a listener who is at rest.What is the apparent frequency heard by the listener? (speed of sound = 340 m/s)

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Question 12

A bat,flying at 7.00 m/s toward a wall,emits a chirp at 50.0 kHz.If the wall reflects this sound pulse,what is the frequency of the echo received by the bat? (v_sound = 340 m/s)

Accepted Answer

The frequency of the echo received by the bat is increased due to the Doppler effect, as the bat is moving towards the wall. The frequency of the echo can be calculated using the formula for the Doppler effect when the source is moving towards a stationary reflector (wall) and then back to the moving detector (bat). The formula for the frequency received $f'$ is given by $f' = f \times \frac{v + v_0}{v - v_s}$, where $f$ is the emitted frequency (50.0 kHz), $v$ is the speed of sound (340 m/s), $v_0$ is the speed of the observer (bat) towards the source (0 m/s, since the wall is stationary and reflects the sound back), and $v_s$ is the speed of the source (bat) towards the observer (7.00 m/s). Substituting the values, we get $f' = 50.0 \times \frac{340 + 7}{340 - 7} = 50.0 \times \frac{347}{333} \approx 52.1 kHz$.

Question 13

You stand by the railroad tracks as a train passes by.You hear a 1 020-Hz frequency when the train approaches,which changes to 760 Hz as it goes away.How fast is the train moving? The speed of sound in air is 340 m/s.

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Question 14

A train station bell gives off a fundamental tone of 500 Hz as the train approaches the station at a speed of 30.0 m/s.If the speed of sound in air is 339 m/s,what will be the apparent frequency of the bell to an observer riding the train?

Accepted Answer

The apparent frequency can be calculated using the Doppler effect formula for sound: f' = f * (v + vo) / (v + vs), where f is the source frequency (500 Hz), v is the speed of sound (339 m/s), vo is the observer's speed (30 m/s), and vs is the source speed (0 m/s, since the bell is stationary). Plugging in the values, f' = 500 * (339 + 30) / 339 = 544 Hz.

Question 15

The Doppler shift of ultrasonic waves can measure the speed of blood in an artery.If the frequency of the stationary source is 95.0 kHz and the reflected sound has a Doppler shift of 210 Hz,what is the blood flow speed? (The speed of sound inside the body is 1 500 m/s. )

Accepted Answer

The Doppler shift formula for sound waves is $\Delta f = \frac{2fv}{v_s}$, where $\Delta f$ is the Doppler shift (210 Hz), $f$ is the frequency of the stationary source (95,000 Hz), $v$ is the speed of the object (blood flow speed, which we are solving for), and $v_s$ is the speed of sound in the medium (1,500 m/s). Rearranging the formula to solve for $v$, we get $v = \frac{\Delta f \cdot v_s}{2f}$. Substituting the given values, $v = \frac{210 \cdot 1500}{2 \cdot 95000}$, which calculates to approximately 1.7 m/s.

Question 16

A plane is traveling at Mach 0.930 through air at a temperature of 0°C.What is the plane's speed? (Speed of sound at 0°C is 331 m/s. )

Accepted Answer

The speed of the plane is calculated by multiplying the Mach number by the speed of sound at the given temperature: 0.930 * 331 m/s = 308 m/s.

Question 17

Two loudspeakers are placed next to each other and driven by the same source at 515 Hz.A listener is positioned in front of the two speakers and on the line separating them,thus creating a constructive interference at the listener's ear.What minimum distance would one of the speakers be moved back away from the listener to produce destructive interference at the listener's ear? (The speed of sound = 340 m/s. )

Accepted Answer

To create constructive interference at the listener's ear, the distance between the two speakers must be an integer multiple of the wavelength of the sound wave. Since the frequency of the source is 515 Hz, the wavelength can be calculated using the formula:

wavelength = speed of sound / frequency

wavelength = 340 m/s / 515 Hz ≈ 0.66 m

Thus, the distance between the two speakers must be an integer multiple of 0.66 m for constructive interference to occur at the listener's ear.

To produce destructive interference, one of the speakers must be moved back by half a wavelength, or 0.33 m. This will make the distance between the two speakers an odd multiple of the wavelength, resulting in destructive interference at the listener's ear. Therefore, the minimum distance that one of the speakers needs to be moved back is 0.33 m.

Hence, the answer is C) 0.33 m.

Question 18

Two cars,one in front of the other,are traveling down the highway at 55.0 m/s.The car behind sounds its horn,which has a frequency of 530 Hz.What is the frequency heard by the driver of the lead car? (v_sound = 340 m/s)

Accepted Answer

Since both cars are moving at the same speed in the same direction, there is no relative velocity between them. Thus, the frequency of the sound heard by the driver of the lead car remains the same as the source frequency, which is 530 Hz.

Question 19

An airplane flying with a constant speed flies from a warm air mass into a cold air mass.The Mach number will

Accepted Answer

The Mach number, which is the ratio of the speed of the airplane to the speed of sound in the surrounding air, will increase when the airplane flies from a warm air mass into a cold air mass. This is because the speed of sound decreases in colder air, assuming the airplane's speed remains constant.

Question 20

When two sound waves are out of phase by ____,destructive interference will occur.

Accepted Answer

Destructive interference occurs when two waves are out of phase by 180° (or an odd multiple of 180°), which is equivalent to 900° (5 times 180°).

Quiz 14: Sound