# Quiz 20: Traveling Waves

Physics & Astronomy

49

All Questions

42

Multiple Choice

1

True False

4

Essay

2

Short Answer

0

Not Answered

Q 1

Four traveling waves are described by the following equations, where all quantities are measured in SI units and y represents the displacement.
I: y = 0.12 cos(3x - 21t)
II: y = 0.15 sin(6x + 42t)
III: y = 0.13 cos(6x + 21t)
IV: y = -0.27 sin(3x - 42t)
Which of these waves have the same period?
A) I and III, and also II and IV
B) I and IV, and also II and III
C) I and II, and also III and IV
D) All of them have the same period.
E) They all have different periods.

Free

Multiple Choice

A

Q 2

Four traveling waves are described by the following equations, where all quantities are measured in SI units and y represents the displacement.
I: y = 0.12 cos(3x + 2t)
II: y = 0.15 sin(6x - 3t)
III: y = 0.23 cos(3x + 6t)
IV: y = -0.29 sin(1.5x - t)
Which of these waves have the same speed?
A) I and III
B) I and IV
C) II and III
D) I and II
E) III and IV

Free

Multiple Choice

B

Q 3

For the wave shown in the figure, the wavelength is
A) 8 m.
B) 4 m.
C) 2 m.
D) 1 m.
E) unable to be determined from the given information.

Free

Multiple Choice

E

Q 4

For the wave shown in the figure, the frequency is
A) 0.5 Hz.
B) 1 Hz.
C) 2 Hz.
D) 4 Hz.
E) unable to be determined from the given information.

Multiple Choice

Q 5

The figure shows the displacement y of a traveling wave at a given position as a function of time and the displacement of the same wave at a given time as a function of position. Determine the wavelength of the wave.
A) 2.0 cm
B) 3.0 m
C) 2.0 m
D) 4.0 m
E) 1.5 m

Multiple Choice

Q 6

The figure shows the displacement y of a wave at a given position as a function of time and the displacement of the same wave at a given time as a function of position. Determine the frequency of the wave.
A) 4.0 Hz
B) 0.50 Hz
C) 3.0 Hz
D) 0.33 Hz
E) 0.25 Hz

Multiple Choice

Q 7

When a weight W is hanging from a light vertical string, the speed of pulses on the string is V. If a second weight W is added without stretching the string, the speed of pulses on this string will now become
A) 2V.
B) V.
C) V.
D) V/ .
E) V/2

Multiple Choice

Q 8

You are generating traveling waves on a stretched string by wiggling one end. If you suddenly begin to wiggle more rapidly without appreciably affecting the tension, you will cause the waves to move down the string
A) faster than before.
B) slower than before.
C) at the same speed as before.

Multiple Choice

Q 9

In the figure, which of the curves best represents the variation of wave speed as a function of tension for transverse waves on a stretched string?
A) A
B) B
C) C
D) D
E) E

Multiple Choice

Q 10

A transverse wave traveling along a string transports energy at a rate r. If we want to double this rate, we could
A) increase the amplitude of the wave by a factor of 8.
B) increase the amplitude of the wave by a factor of 4.
C) increase the amplitude of the wave by a factor of 2.
D) increase the amplitude by a factor of .
E) increase the amplitude by a factor of .

Multiple Choice

Q 11

Which one of the following statements is true?
A) Both the intensity level (in dB) and the sound intensity can never be negative.
B) The intensity level (in dB) obeys an inverse-square distance law, but the sound intensity does not.
C) Both intensity level (in dB) and sound intensity obey inverse-square distance laws.
D) The sound intensity can never be negative, but the intensity level (in dB) can be negative.
E) Both the intensity level (in dB) and the sound intensity can be negative.

Multiple Choice

Q 12

When a rocket is traveling toward a mountain at 100 m/s, the sound waves from this rocket's engine approach the mountain at speed V. If the rocket doubles its speed to 200 m/s, the sound waves from the engine will now approach the mountain at speed
A) 4V.
B) 2V.
C) V.
D) V.

Multiple Choice

Q 13

A plane flies toward a stationary siren at 1/4 the speed of sound. Then the plane stands still on the ground and the siren is driven toward it at 1/4 the speed of sound. In both cases, a person sitting in the plane will hear the same frequency of sound from the siren.

True False

Q 14

A stationary siren emits sound of frequency 1000 Hz and wavelength 0.343 m. An observer who is moving toward the siren will measure a frequency f and wavelength λ for this sound such that
A) f > 1000 Hz and λ > 0.343 m.
B) f > 1000 Hz and λ = 0.343 m.
C) f > 1000 Hz and λ < 0.343 m.
D) f = 1000 Hz and λ < 0.343 m.

Multiple Choice

Q 15

The figure shows the displacement y of a traveling wave at a given position as a function of time and the displacement of the same wave at a given time as a function of position. How fast is the wave traveling?
A) 3.0 m/s
B) 0.75 m/s
C) 0.66 m/s
D) 1.5 m/s
E) 2.0 m/s

Multiple Choice

Q 16

Ocean tides are waves that have a period of 12 hours, an amplitude (in some places) of 1.50 m, and a speed of 750 km/hr. What is the distance between adjacent crests of these waves?
A) 9000 km
B) 32,400 km
C) 9000 m
D) 32,400 m
E) 2500 m

Multiple Choice

Q 17

The vertical displacement y(x,t) of a string stretched along the horizontal x-axis is given by
y(x,t) = (6.00 mm) cos[(3.25 m

^{-1})x - (7.22 rad/s)t]. (a) What is the minimum time for each complete cycle of the wave? (b) What is the distance between adjacent crests of the wave? (c) How fast does this wave travel? Essay

Q 18

A transverse wave is traveling on a string stretched along the horizontal x-axis. The equation for the vertical displacement y of the string is given by y = 0.0020 cos[π(15x - 52t)], where all quantities are in SI units. The maximum speed of a particle of the string is closest to
A) 0.33 m/s.
B) 0.43 m/s.
C) 0.53 m/s.
D) 0.64 m/s.
E) 0.74 m/s.

Multiple Choice

Q 19

Find the speed of an ocean wave whose vertical displacement y as a function of time t is given by y(x,t) = 3.7 cos(2.2x - 5.6t), where all quantities are in SI units.
A) 2.5 m/s
B) 1.9 m/s
C) 3.5 m/s
D) 4.5 m/s

Multiple Choice

Q 20

You and your surfing buddy are waiting to catch a wave a few hundred meters off the beach. The waves are conveniently sinusoidal, and you notice that when you're on the top of one wave and moving toward your friend, she is exactly halfway between you and the trough of the wave. 1.50 seconds later, your friend is at the top of the wave. You estimate the horizontal distance between you and your friend at 8.00 m.
(a) What is the frequency of the waves?
(b) Find the speed of the waves.

Essay

Q 21

Waves travel along a 100-m length of string which has a mass of 55 g and is held taut with a tension of 75 N. What is the speed of the waves?
A) 3700 m/s
B) 370 m/s
C) 37 m/s
D) 0.37 m/s
E) 3.7 m/s

Multiple Choice

Q 22

A 6.00-m long rope is under a tension of 600 N. Waves travel along this rope at 40.0 m/s. What is the mass of the rope?
A) 1.00 kg
B) 1.25 kg
C) 2.25 kg
D) 2.50 kg
E) 1.12 kg

Multiple Choice

Q 23

The density of aluminum is 2700 kg/m

^{3}. If transverse waves propagate at 34 ,s in a 4.6-mm diameter aluminum wire, what is the tension on the wire? A) 52 N B) 31 N C) 42 N D) 62 N Multiple Choice

Q 24

A 6.0-m wire with a mass of 50 g, is under tension. A transverse wave, for which the frequency is 810 Hz, the wavelength is 0.40 m, and the amplitude is 4.0 mm, is propagating on the wire. The time for a crest of this wave to travel the length of the wire is closest to
A) 19 ms.
B) 16 ms.
C) 21 ms.
D) 23 ms.
E) 25 ms.

Multiple Choice

Q 25

A 8.0-m long wire with a mass of 10 g is under tension. A transverse wave for which the frequency is 570 Hz, the wavelength is 0.10 m, and the amplitude is 3.7 mm is propagating on the wire. The maximum transverse acceleration of a point on a wire is closest to
A) 47,000 m/s

^{2}. B) 41,000 m/s^{2}. C) 35,000 m/s^{2}. D) 29,000 m/s^{2}. E) 53,000 m/s^{2}. Multiple Choice

Q 26

A heavy stone of mass m is hung from the ceiling by a thin 8.25-g wire that is 65.0 cm long. When you gently pluck the upper end of the wire, a pulse travels down the wire and returns 7.84 ms later, having reflected off the lower end. The stone is heavy enough to prevent the lower end of the wire from moving. What is the mass m of the stone?
A) 8.90 kg
B) 23.1 kg
C) 35.6 kg
D) 227 kg
E) 349 kg

Multiple Choice

Q 27

Two people are talking at a distance of 3.0 m from where you are and you measure the sound intensity as 1.1 × 10

^{-7}W/m^{2}. Another student is 4.0 m away from the talkers. What sound intensity does the other student measure? Assume that the sound spreads out uniformly and undergoes no significant reflections or absorption. A) 6.2 × 10^{-8}W/m^{2}B) 1.5 × 10^{-7}W/m^{2}C) 8.3 × 10^{-8}W/m^{2}D) 7.8 × 10^{-7}W/m^{2}E) 2.5 × 10^{-8}W/m^{2} Multiple Choice

Q 28

Calculate the light intensity 1.51 m from a light bulb that emits 100 W of visible light, assuming that the light radiates uniformly in all directions.
A) 3.49 W/m

^{2}B) 4.01 W/m^{2}C) 43.9 W/m^{2}D) 50.5 W/m^{2} Multiple Choice

Q 29

The intensity of sunlight falling on the earth is about 1.4 kW/m

^{2}(before any gets absorbed by our atmosphere). At what rate does the sun emit light energy? (The earth-sun distance = 1.5 × 10^{8}km and the earth's radius = 6.4 × 10^{3}km.) A) 4.0 × 10^{26}W B) 3.2 × 10^{22}W C) 7.2 × 10^{14}W D) 7.6 × 10^{8}W Multiple Choice

Q 30

Observer A is 3.0 m from a tiny light bulb and observer B is 12.0 m from the same bulb. Assume that the light spreads out uniformly and undergoes no significant reflections or absorption. If observer B sees a light of intensity I, the light intensity that A sees is
A) I.
B) 9I.
C) 16I.
D) 36I.
E) 144I.

Multiple Choice

Q 31

A tiny vibrating source sends waves uniformly in all directions. An area of 3.25 cm

^{2}on a sphere of radius 2.50 m centered on the source receives energy at a rate of 4.20 J/s. (a) What is the intensity of the waves at 2.50 m from the source and at 10.0 m from the source? (b) At what rate is energy leaving the vibrating source of the waves? Essay

Q 32

A certain source of sound waves radiates uniformly in all directions. At a distance of 20 m from the source the intensity level is 51 db. What is the total acoustic power output of the source, in watts? (Note: The reference intensity I

_{0}is 1.0 × 10^{-12}W/m^{2}.) Short Answer

Q 33

A howler monkey is the loudest land animal and, under some circumstances, can be heard up to a distance of 5.0 km. Assume the acoustic output of a howler to be uniform in all directions and that the threshold of hearing is 1.0 × 10

^{-12}W/m^{2}. The acoustic power emitted by the howler is closest to A) 0.31 mW. B) 0.11 mW. C) 1.1 mW. D) 3.2 mW. E) 11 mW. Multiple Choice

Q 34

The howler monkey is the loudest land animal and, under some circumstances, can be heard up to a distance of 8.9 km. Assume the acoustic output of a howler to be uniform in all directions and that the threshold of hearing is 1.0 × 10

^{-12}W/m^{2}. A juvenile howler monkey has an acoustic output of 63 µW. What is the ratio of the acoustic intensity produced by the juvenile howler to the reference intensity I_{0}, at a distance of 210 m? A) 110 B) 230 C) 76 D) 170 E) 300 Multiple Choice

Q 35

An enclosed chamber with sound absorbing walls has a 2.0 m × 1.0 m opening for an outside window. A loudspeaker is located outdoors,, 78 m away and facing the window. The intensity level of the sound entering the window space from the loudspeaker is 79 dB. Assume the acoustic output of the loudspeaker is uniform in all directions and that the acoustic energy incident upon the ground is completely absorbed and therefore is not reflected into the window. The threshold of hearing is 1.0 × 10

^{-12}W/m^{2}. The acoustic power entering through the window space is closest to A) 160 µW. B) 79 µW. C) 320 µW. D) 790 µW. E) 1600 µW. Multiple Choice

Q 36

An enclosed chamber with sound absorbing walls has a 2.0 m × 1.0 m opening for an outside window. A loudspeaker is located outdoors, 84 m away and facing the window. The intensity level of the sound entering the window space from the loudspeaker is 56 dB. Assume the acoustic output of the loudspeaker is uniform in all directions and that acoustic energy incident upon the ground is completely absorbed and therefore is not reflected into the window. The threshold of hearing is 1.0 × 10

^{-12}W/m^{2}. The acoustic power output of the loudspeaker is closest to A) 0.035 W. B) 0.070 W. C) 0.18 W. D) 0.35 W. E) 0.70 W. Multiple Choice

Q 37

A sound source emits 20.0 W of acoustical power spread equally in all directions. The threshold of hearing is 1.0 × 10

^{-12}W/m^{2}. What is the sound intensity level 30.0 m from the source? A) 92.5 dB B) 81.5 dB C) 1.77 × 10^{-3}dB D) 1.77 × 10^{-3}W E) -27.5 dB Multiple Choice

Q 38

The sound level at 1.0 m from a certain talking person talking is 60 dB. You are surrounded by five such people, all 1.0 m from you and all talking equally loud at the same time. The threshold of hearing is 1.0 × 10

^{-12}W/m^{2}. What sound level are you being exposed to? You can neglect any absorption, reflection, or interference of the sound. The threshold of hearing is 1.0 × 10^{-12}W/m^{2}. A) 300 dB B) 60 dB C) 74 dB D) 67 dB E) 81 dB Multiple Choice

Q 39

A certain crying baby emits sound with an intensity of 8.0 × 10

^{-8}W/m^{2}. What is the intensity level due to a set of five such crying babies, all crying with the same intensity? You can neglect any absorption, reflection, or interference of the sound. The lowest detectable intensity is 1.0 × 10^{-12}W/m^{2}. A) 79 dB B) 69 dB C) 56 dB D) 49 dB E) 36 dB Multiple Choice

Q 40

The intensity level of a "Super-Silent" power lawn mower at a distance of 1.0 m is 100 dB. You wake up one morning to find that four of your neighbors are all mowing their lawns using identical "Super-Silent" mowers. When they are each 20 m from your open bedroom window, what is the intensity level of the sound in your bedroom? You can neglect any absorption, reflection, or interference of the sound. The lowest detectable intensity is 1.0 × 10

^{-12}W/m^{2}. A) 80 dB B) 104 dB C) 400 dB D) 50 dB E) 40 dB Multiple Choice

Q 41

If the intensity level at distance d of one trombone is 70 dB, what is the intensity level of 76 identical trombones, all at distance d?
A) 146 dB
B) 89 dB
C) 5320 dB
D) 76 dB
E) 82 dB

Multiple Choice

Q 42

At a distance of 2.00 m from a point source of sound, the intensity level is 80.0 dB. What will be the intensity level at a distance of 4.00 m from this source? The lowest detectable intensity is 1.0 × 10

^{-12}W/m^{2}. A) 77.0 dB B) 74.0 dB C) 60.0 dB D) 40.0 dB E) 20.0 dB Multiple Choice

Q 43

A woman is riding a bicycle at 18.0 m/s along a straight road that runs parallel to and right next to some railroad tracks. She hears the whistle of a train that is behind. The frequency emitted by the train is 840 Hz, but the frequency the woman hears is 778 Hz. Take the speed of sound to be 340 m/s.
(a) What is the speed of the train, and is the train traveling away from or toward the bicycle?
(b) What frequency is heard by a stationary observer located between the train and the bicycle?

Essay

Q 44

A factory siren indicating the end of a shift has a frequency of 90.0 Hz. The speed of sound is 343 m/s.
(a) What frequency is perceived by the occupant of a car traveling towards the factory at 25.0 m/s?
(b) What frequency is perceived by the occupant of a car traveling away from the factory at 30.0 m/s?

Short Answer

Q 45

As you stand by the side of the road, a car approaches you at a constant speed, sounding its horn, and you hear a frequency of 80.0 Hz. After the car goes by, you hear a frequency of 60.0 Hz. What is the speed of the car? The speed of sound in the air is 343 m/s.
A) 64.0 m/s
B) 49.0 m/s
C) 16.0 m/s
D) 36.0 m/s
E) 25.0 m/s

Multiple Choice

Q 46

A boy on a bicycle approaches a brick wall as he sounds his horn at a frequency 400.00 Hz. The sound he hears reflected back from the wall is at a frequency 408.00 Hz. At what is the speed is the boy riding his bicycle toward the wall? Assume the speed of sound in air is 340 m/s.
A) 3.68 m/s
B) 333 m/s
C) 6.67 m/s
D) 6.80 m/s
E) 3.37 m/s

Multiple Choice

Q 47

You are driving along a highway at 35.0 m/s when you hear the siren of a police car approaching you from behind and you perceive the frequency as 1370 Hz. You are relieved that he is in pursuit of a different speeder when he continues past you, but now you perceive the frequency as 1330 Hz. What is the speed of the police car? The speed of sound in air is 343 m/s.
A) 38.4 m/s
B) 30.0 m/s
C) 39.2 m/s
D) 40.0 m/s
E) 41.7 m/s

Multiple Choice

Q 48

You are driving along a highway at 35.0 m/s when you hear the siren of a police car approaching you from behind and you perceive the frequency as 1310 Hz. You are relieved that he is in pursuit of a different speeder when he continues past you, but now you perceive the frequency as 1240 Hz. What is the frequency of the siren in the police car? The speed of sound in air is 343 m/s.
A) 1300 Hz
B) 1320 Hz
C) 1270 Hz
D) 1360 Hz
E) 1370 Hz

Multiple Choice

Q 49

A carousel that is 5.00 m in radius has a pair of 600-Hz sirens mounted on posts at opposite ends of a diameter. The carousel rotates with an angular velocity of 0.800 rad/s. A stationary listener is located at a distance from the carousel. The speed of sound is 350 m/s. The longest wavelength reaching the listener from the sirens is closest to
A) 57.0 cm.
B) 57.7 cm.
C) 58.3 cm.
D) 59.0 cm.
E) 59.6 cm.

Multiple Choice