Question 1

What is the intensity level in decibels of a sound with intensity 10-3 W/m2? The threshold of human hearing is 1.0 × 10-12 W/m2.

Accepted Answer

A)  30 dB 
B)  60 dB 
C)  90 dB 
D)  96 dB 
A)  30 dB 
B)  60 dB 
C)  90 dB 
D)  96 dB

Question 2

A certain factory whistle can be heard up to a distance of 9.8 km. Assuming that the acoustic output of the whistle is uniform in all directions, at what distance from the factory is the intensity level of the whistle sound equal to 25 dB? The threshold of human hearing is 1.0 × 10-12 W/m2.

Accepted Answer

A)  550 m 
B)  660 m 
C)  830 m 
D)  940 m 
E)  1100 m 
A)  550 m 
B)  660 m 
C)  830 m 
D)  940 m 
E)  1100 m

Question 3

A bat emits a sound at a frequency of 39.0 kHz as it approaches a wall. The bat detects beats with a frequency of 827 Hz between the sound it emits and the echo bouncing from the wall. What is the speed of the bat if the speed of sound in air is 343 m/s?

Accepted Answer

A)  2.7 m/s 
B)  3.0 m/s 
C)  3.6 m/s 
D)  5.4 m/s 
E)  9.0 m/s 
A)  2.7 m/s 
B)  3.0 m/s 
C)  3.6 m/s 
D)  5.4 m/s 
E)  9.0 m/s

Question 4

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 power emitted by the source?

Accepted Answer

A)  2.1 × 10-8 W 
B)  2.7 × 10-7 W 
C)  2.1 × 10-6 W 
D)  2.7 × 10-5 W 
A)  2.1 × 10-8 W 
B)  2.7 × 10-7 W 
C)  2.1 × 10-6 W 
D)  2.7 × 10-5 W

Question 5

You double your distance from a sound source that is radiating equally in all directions. What happens to the intensity of the sound? It reduces to

Accepted Answer

A)  one-half its original value. 
B)  one-fourth its original value. 
C)  one-sixteenth its original value. 
D)  none of the above 
A)  one-half its original value. 
B)  one-fourth its original value. 
C)  one-sixteenth its original value. 
D)  none of the above

Question 6

If the intensity level of one trombone is 70 dB, calculate a reasonable estimate for the intensity level of 76 trombones all playing simultaneously in the same place?

Accepted Answer

A)  146 dB 
B)  89 dB 
C)  70 dB 
D)  76 dB 
E)  82 dB 
A)  146 dB 
B)  89 dB 
C)  70 dB 
D)  76 dB 
E)  82 dB

Question 7

A wave whose wavelength is 0.500 m is traveling down a 500-m long wire whose total mass is 25 kg and is under a tension of 2000 N.
(a) What is the speed of the wave on the wire?
(b) Find the frequency of this wave.

Accepted Answer

(a) 200 m/

Question 8

A crane lifts a 2500-kg beam at a steady rate of 15 cm/s using a steel cable whose mass per unit length is 0.65 kg/m. What is the speed of transverse waves on this cable?

Accepted Answer

A)  230 m/s 
B)  580 m/s 
C)  1200 m/s 
D)  1900 m/s 
E)  190 m/s 
A)  230 m/s 
B)  580 m/s 
C)  1200 m/s 
D)  1900 m/s 
E)  190 m/s

Question 9

Two in-phase loudspeakers are some distance apart. They emit sound with a frequency of 536 Hz. A microphone is moved between the speakers along the line joining the two speakers with a constant speed of 1.60 m/s. What beat frequency is observed? The speed of sound in air is 343 m/s.

Accepted Answer

A)  5.00 Hz 
B)  6.00 Hz 
C)  7.00 Hz 
D)  8.00 Hz 
E)  9.00 Hz 
A)  5.00 Hz 
B)  6.00 Hz 
C)  7.00 Hz 
D)  8.00 Hz 
E)  9.00 Hz

Question 10

A crying baby emits sound with an intensity of 8.0 × 10-8 W/m2. Calculate a reasonable estimate for the intensity level from a set of quintuplets (five babies), all crying simultaneously at the same place? The lowest detectable intensity is 1.0 × 10-12 W/m2.

Accepted Answer

A)  79 dB 
B)  69 dB 
C)  56 dB 
D)  49 dB 
E)  36 dB 
A)  79 dB 
B)  69 dB 
C)  56 dB 
D)  49 dB 
E)  36 dB

Question 11

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

A)  1.54 s 
B)  1.43 s 
C)  1.66 s 
D)  1.79 s 
A)  1.54 s 
B)  1.43 s 
C)  1.66 s 
D)  1.79 s

Question 12

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

A)  67 dB 
B)  13 dB 
C)  44 dB 
D)  88 dB 
A)  67 dB 
B)  13 dB 
C)  44 dB 
D)  88 dB

Question 13

The sound from the whistle of a truck moving at 17.0 m/s toward a cliff reflects from the cliff and is heard by the driver of the truck. When it is parked at the side of the road, the whistle from the truck produces sound of frequency 2.267 kHz. As observed by the driver of the truck, what is the change in frequency the sound from the whistle due to the reflection? The speed of sound is 343 m/s.

Accepted Answer

A)  236 Hz 
B)  228 Hz 
C)  207 Hz 
D)  118 Hz 
E)  472 Hz 
A)  236 Hz 
B)  228 Hz 
C)  207 Hz 
D)  118 Hz 
E)  472 Hz

Question 14

Crests of an ocean wave pass a pier every $10.0 \mathrm {~s}$ If the waves are moving at $5.6 \mathrm {~m} / \mathrm { s }$ what is the wavelength of the ocean waves?

Accepted Answer

A)  56 m 
B)  28 m 
C)  64 m 
D)  48 m 
A)  56 m 
B)  28 m 
C)  64 m 
D)  48 m

Question 15

A car approaches you at a constant speed, sounding its horn, and you hear a frequency of 76 Hz. After the car goes by, you hear a frequency of 65 Hz. What is the frequency of the sound emitted by the horn? The speed of sound in the air is 343 m/s.

Accepted Answer

A)  68 Hz 
B)  69 Hz 
C)  70 Hz 
D)  71 Hz 
E)  72 Hz 
A)  68 Hz 
B)  69 Hz 
C)  70 Hz 
D)  71 Hz 
E)  72 Hz

Question 16

A police car has an 800-Hz siren. It is traveling at 35.0 m/s on a day when the speed of sound through air is 340 m/s. The car approaches and passes an observer who is standing along the roadside. What change of frequency does the observer hear?

Accepted Answer

A)  0 Hz 
B)  82 HZ 
C)  166 Hz 
D)  249 Hz 
A)  0 Hz 
B)  82 HZ 
C)  166 Hz 
D)  249 Hz

Question 17

When a certain string is under tension T, the speed of a wave in the string is v. What will be the speed of a wave in the string if the tension is increased to 2T without changing the mass or length of the string?

Accepted Answer

A)  v/2 
B)  v/ $\sqrt { 2 }$ 
C)  v $\sqrt { 2 }$ 
D)  2v 
E)  4v 
A)  v/2 
B)  v/ $\sqrt { 2 }$ 
C)  v $\sqrt { 2 }$ 
D)  2v 
E)  4v

Question 18

Four waves are described by the following equations, where distances are measured in meters and times in seconds. 
I. y = 0.12 cos(3x - 21t)
II. y = 0.15 sin(6x + 42t)
III. y = 0.13 cos(6x + 21t)
IV. y = -0.23 sin(3x - 42t)
Which of these waves have the same speed?

Accepted Answer

A)  I and II 
B)  I and III 
C)  II and III 
D)  III and IV 
E)  II and IV 
A)  I and II 
B)  I and III 
C)  II and III 
D)  III and IV 
E)  II and IV

Question 19

The density of aluminum is 2700 kg/m3. If transverse waves travel at $38 \mathrm {~m} / \mathrm { s }$ in an aluminum wire of diameter $4.6 \mathrm {~mm}$ what is the tension on the wire?

Accepted Answer

A)  65 N 
B)  39 N 
C)  52 N 
D)  78 N 
A)  65 N 
B)  39 N 
C)  52 N 
D)  78 N

Question 20

What is the frequency of a pressure wave of wavelength 2.5 m that is traveling at 1400 m/s?

Accepted Answer

A)  178 Hz 
B)  1.78 kHz 
C)  560 Hz 
D)  5.6 kHz 
A)  178 Hz 
B)  1.78 kHz 
C)  560 Hz 
D)  5.6 kHz

Exam 15: Traveling Waves and Sound

What is the intensity level in decibels of a sound with intensity 10-3 W/m2? The threshold of human hearing is 1.0 × 10-12 W/m2.

A certain factory whistle can be heard up to a distance of 9.8 km. Assuming that the acoustic output of the whistle is uniform in all directions, at what distance from the factory is the intensity level of the whistle sound equal to 25 dB? The threshold of human hearing is 1.0 × 10-12 W/m2.

A bat emits a sound at a frequency of 39.0 kHz as it approaches a wall. The bat detects beats with a frequency of 827 Hz between the sound it emits and the echo bouncing from the wall. What is the speed of the bat if the speed of sound in air is 343 m/s?

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 power emitted by the source?

You double your distance from a sound source that is radiating equally in all directions. What happens to the intensity of the sound? It reduces to

If the intensity level of one trombone is 70 dB, calculate a reasonable estimate for the intensity level of 76 trombones all playing simultaneously in the same place?

A wave whose wavelength is 0.500 m is traveling down a 500-m long wire whose total mass is 25 kg and is under a tension of 2000 N. (a) What is the speed of the wave on the wire? (b) Find the frequency of this wave.

A crane lifts a 2500-kg beam at a steady rate of 15 cm/s using a steel cable whose mass per unit length is 0.65 kg/m. What is the speed of transverse waves on this cable?

Two in-phase loudspeakers are some distance apart. They emit sound with a frequency of 536 Hz. A microphone is moved between the speakers along the line joining the two speakers with a constant speed of 1.60 m/s. What beat frequency is observed? The speed of sound in air is 343 m/s.

A crying baby emits sound with an intensity of 8.0 × 10-8 W/m2. Calculate a reasonable estimate for the intensity level from a set of quintuplets (five babies), all crying simultaneously at the same place? The lowest detectable intensity is 1.0 × 10-12 W/m2.

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?

Crests of an ocean wave pass a pier every 10.0 s10.0 \mathrm {~s}10.0 s If the waves are moving at 5.6 m/s5.6 \mathrm {~m} / \mathrm { s }5.6 m/s what is the wavelength of the ocean waves?

A car approaches you at a constant speed, sounding its horn, and you hear a frequency of 76 Hz. After the car goes by, you hear a frequency of 65 Hz. What is the frequency of the sound emitted by the horn? The speed of sound in the air is 343 m/s.

A police car has an 800-Hz siren. It is traveling at 35.0 m/s on a day when the speed of sound through air is 340 m/s. The car approaches and passes an observer who is standing along the roadside. What change of frequency does the observer hear?

When a certain string is under tension T, the speed of a wave in the string is v. What will be the speed of a wave in the string if the tension is increased to 2T without changing the mass or length of the string?

Four waves are described by the following equations, where distances are measured in meters and times in seconds. I. y = 0.12 cos(3x - 21t) II. y = 0.15 sin(6x + 42t) III. y = 0.13 cos(6x + 21t) IV. y = -0.23 sin(3x - 42t) Which of these waves have the same speed?

The density of aluminum is 2700 kg/m3. If transverse waves travel at 38 m/s38 \mathrm {~m} / \mathrm { s }38 m/s in an aluminum wire of diameter 4.6 mm4.6 \mathrm {~mm}4.6 mm what is the tension on the wire?

What is the frequency of a pressure wave of wavelength 2.5 m that is traveling at 1400 m/s?

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What is the intensity level in decibels of a sound with intensity 10^-3 W/m²? The threshold of human hearing is 1.0 × 10^-12 W/m².

A certain factory whistle can be heard up to a distance of 9.8 km. Assuming that the acoustic output of the whistle is uniform in all directions, at what distance from the factory is the intensity level of the whistle sound equal to 25 dB? The threshold of human hearing is 1.0 × 10^-12 W/m².

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 power emitted by the source?

A crying baby emits sound with an intensity of 8.0 × 10^-8 W/m². Calculate a reasonable estimate for the intensity level from a set of quintuplets (five babies), all crying simultaneously at the same place? The lowest detectable intensity is 1.0 × 10^-12 W/m².

Crests of an ocean wave pass a pier every $10.0 \mathrm {~s}$ If the waves are moving at $5.6 \mathrm {~m} / \mathrm { s }$ what is the wavelength of the ocean waves?

The density of aluminum is 2700 kg/m³. If transverse waves travel at $38 \mathrm {~m} / \mathrm { s }$ in an aluminum wire of diameter $4.6 \mathrm {~mm}$ what is the tension on the wire?