Quiz 14

Two harmonic waves traveling in opposite directions interfere to produce a standing wave described by y = 2 sin (4x) cos (3t) where x is in m and t is in s. What is the speed (in m/s) of the interfering waves? Question options: 1) 0.75 2) 0.25 3) 1.3 4) 12 5) 3.0

1) 0.75

For the wave described by y = 0.02 sin (kx) at t = 0 s, the first maximum at a positive x coordinate occurs where x = 4 m. Where on the positive x axis does the second maximum occur? Question options: 1) 20 m 2) 18 m 3) 24 m 4) 28 m 5) 16 m

1) 20 m

Transverse waves are traveling on a 1.00-m long piano string at 500 m/s. If the points of zero vibration occur at one-half wavelength, (where the string is fastened at both ends), find the frequency of vibration. Question options: 1) 250 Hz 2) 500 Hz 3) 1000 Hz 4) 2000 Hz 5) 2500 Hz

1) 250 Hz

Two instruments produce a beat frequency of 5 Hz. If one has a frequency of 264 Hz, what could be the frequency of the other instrument? Question options: 1) 269 Hz 2) 254 Hz 3) 264 Hz 4) 5 Hz 5) 274 Hz

1) 269 Hz

Two harmonic waves traveling in opposite directions interfere to produce a standing wave described by y = 3 sin (2x) cos 5t where x is in m and t is in s. What is the wavelength of the interfering waves? Question options: 1) 3.14 m 2) 1.00 m 3) 6.28 m 4) 12.0 m 5) 2.00 m

1) 3.14 m

If y = 0.02 sin (30x - 400t) (SI units), the wave number is Question options: 1) 30 m-1 2) 30/2p m-1 3) 400/2p m-1 4) 400 m-1 5) 60p m-1

1) 30 m-1

A point source emits sound with a power output of 100 watts. What is the intensity (in W/m2) at a distance of 10.0 m from the source? Question options: 1) 7.96 ´ 10-2 2) 7.96 ´ 10-1 3) 7.96 ´ 100 4) 7.96 ´ 101 5) 7.96 ´ 10-3

1) 7.96 ´ 10-2

The path difference between two waves is 5m. If the wavelength of the waves emitted by the two sources is 4m, what is the phase difference (in degrees)? Question options: 1) 90 2) 400 3) 1.57 4) 7.85 5) 15

1) 90

Four wave functions are given below. Rank the wave functions in order of the magnitude of the frequencies of the waves, from least to greatest. I. y(x, t) = 5sin(4x - 20t + 4) II. y(x, t) = 5sin(3x - 12t + 5) III. y(x, t) = 5cos(4x + 24t + 6) IV. y(x, t) = 14cos(2x - 8t + 3) Question options: 1) IV, II, I, III 2) IV = II, I, III 3) III, I, II, IV 4) IV, I, II, III 5) III, IV, II, I

1) IV, II, I, III

If y = 0.02 sin (30x - 400t) (SI units), the wavelength of the wave is Question options: 1) p/15 m 2) 15/p m 3) 60p m 4) 4.2 m 5) 30 m

1) p/15 m

Write the equation of a wave, traveling along the +x axis with an amplitude of 0.02 m, a frequency of 440 Hz, and a speed of 330 m/sec. Question options: 1) y = 0.02 sin [880p (x/330 - t)] 2) y = 0.02 cos [880p x/330 - 440t] 3) y = 0.02 sin [880p(x/330 + t)] 4) y = 0.02 sin [2p(x/330 + 440t)] 5) y = 0.02 cos [2p(x/330 + 440t)]

1) y = 0.02 sin [880p (x/330 - t)]

Two harmonic waves traveling in opposite directions interfere to produce a standing wave described by y = 4 sin (5x) cos (6t) where x is in m and t is in s. What is the approximate frequency of the interfering waves? Question options: 1) 3 Hz 2) 1 Hz 3) 6 Hz 4) 12 Hz 5) 5 Hz

2) 1 Hz

Determine the intensity (in W/m2) of a harmonic longitudinal wave with a pressure amplitude of 8 ´ 10-3 N/m2 propagating down a tube filled with helium. (r = 0.179 kg/m3, v = 972 m/s.) Question options: 1) 3.7 ´ 10-7 2) 1.8 ´ 10-7 3) 9.2 ´ 10-8 4) 4.6 ´ 10-8 5) 1.5 ´ 10-9

2) 1.8 ´ 10-7

A 100-m long transmission cable is suspended between two towers. If the mass density is 2.01 kg/m and the tension in the cable is 3.00 ´ 104 N, what is the speed of transverse waves on the cable? Question options: 1) 60 m/s 2) 122 m/s 3) 244 m/s 4) 310 m/s 5) 1500 m/s

2) 122 m/s

Ocean waves with a wavelength of 120 m are coming in at a rate of 8 per minute. What is their speed? Question options: 1) 8.0 m/s 2) 16 m/s 3) 24 m/s 4) 30 m/s 5) 4.0 m/s

2) 16 m/s

Two tuning forks with frequencies 264 and 262 Hz produce "beats". What is the beat frequency (in Hz)? Question options: 1) 4 2) 2 3) 1 4) 3 5) 0 (no beats are produced)

2) 2

If y = 0.02 sin (30x - 400t) (SI units) and if the mass density of the string on which the wave propagates is .005 kg/m, then the transmitted power is Question options: 1) 1.03 W 2) 2.13 W 3) 4.84 W 4) 5.54 W 5) 106 W

2) 2.13 W

Calculate the displacement amplitude (in m) of a 20 kHz sound wave in helium if it has a pressure amplitude of 8 ´ 10-3 N/m2. (r = 0.179 kg/m3, v = 972 m/s.) Question options: 1) 2.9 ´ 10-10 2) 3.7 ´ 10-10 3) 7.8 ´ 10-9 4) 2.4 ´ 10-9 5) 1.9 ´ 10-10

2) 3.7 ´ 10-10

A sculptor strikes a piece of marble with a hammer. Find the speed of sound through the marble (in km/s). (The Young's modulus is 50 ´ 109 N/m2 and its density is 2.7 ´ 103 kg/m3.) Question options: 1) 5.1 2) 4.3 3) 3.5 4) 1.3 5) 1.8

2) 4.3

If y = 0.02 sin (30x - 400t) (SI units), the velocity of the wave is Question options: 1) 3/40 m/s 2) 40/3 m/s 3) 60p/400 m/s 4) 400/60p m/s 5) 400 m/s

2) 40/3 m/s

A string is stretched and fixed at both ends, 200 cm apart. If the density of the string is 0.015 g/cm, and its tension is 600 N, what is the wavelength (in cm) of the first harmonic? Question options: 1) 600 2) 400 3) 800 4) 1000 5) 200

2) 400

The variation in the pressure of helium gas, measured from its equilibrium value, is given by DP = 2.9 ´ 10-5 cos (6.2x - 3000t) where x and t have units m and s, and DP is measured in N/m2. Determine the frequency (in Hz) of the wave. Question options: 1) 1500 2) 477 3) 1.01 4) 0.32 5) 239

2) 477

How fast (in m/s) is the Concorde moving if it reaches Mach 1.5? (The speed of sound in air is 344 m/s.) Question options: 1) 229 2) 516 3) 416 4) 728 5) 858

2) 516

A piano string of density 0.0050 kg/m is under a tension of 1350 N. Find the velocity with which a wave travels on the string. Question options: 1) 260 m/s 2) 520 m/s 3) 1040 m/s 4) 2080 m/s 5) 4160 m/s

2) 520 m/s

A truck moving at 36 m/s passes a police car moving at 45 m/s in the opposite direction. If the frequency of the siren relative to the police car is 500 Hz, what is the frequency heard by an observer in the truck as the police car approaches the truck? (The speed of sound in air is 343 m/s.) Question options: 1) 396 2) 636 3) 361 4) 393 5) 617

2) 636

An organ pipe open at both ends has a radius of 4.0 cm and a length of 6.0 m. What is the frequency (in Hz) of the third harmonic? (Assume the velocity of sound is 344 m/s.) Question options: 1) 76 2) 86 3) 54 4) 28 5) 129

2) 86

Four wave functions are given below.Rank the wave functions in order of the magnitude of the wave speeds, from least to greatest. I. y(x, t) = 5sin(4x - 20t + 4) II. y(x, t) = 5sin(3x - 12t + 5) III. y(x, t) = 5cos(4x + 24t + 6) IV. y(x, t) = 14cos(2x - 8t + 3) Question options: 1) IV, II, I, III 2) IV = II, I, III 3) III, I, II, IV 4) IV, I, II, III 5) III, IV, II, I

2) IV = II, I, III

Do not try the following: it could kill you. This question is only about a hypothetical possibility.) If you were standing below an object falling at terminal velocity, as it approached you, you would hear the sound Question options: 1) drop in frequency. 2) stay at the same frequency. 3) increase in frequency. 4) decrease in loudness. 5) stay at the same loudness.

2) stay at the same frequency

You are holding on to one end of a long string that is fastened to a rigid steel light pole. After producing a wave pulse that was 5 mm high and 4 cm wide, you want to produce a pulse that is 6 cm wide but still 5 mm high. You must move your hand up and down once, Question options: 1) the same distance up as before, but take a shorter time. 2) the same distance up as before, but take a longer time. 3) a smaller distance up, but take a shorter time. 4) a greater distance up, but take a longer time. 5) a greater distance up, but take the same time.

2) the same distance up as before, but take a longer time.

When you hear the horn of a car that is approaching you, the frequency that you hear is larger than that heard by a person in the car because Question options: 1) wave crests are farther apart by the distance the car travels in one period. 2) wave crests are closer together by the distance the car travels in one period. 3) the car gets ahead of each wave crest before it emits the next one. 4) the speed of sound in air is increased by the speed of the car. 5) a speeding car emits more wavecrests in each period.

2) wave crests are closer together by the distance the car travels in one period.

The lowest A on a piano has a frequency of 27.5 Hz. If the tension in the 2.00-m string is 308 N, and one-half wavelength occupies the string, what is the mass of the wire? Question options: 1) 0.025 kg 2) 0.049 kg 3) 0.051 kg 4) 0.081 kg 5) 0.037 kg

3) 0.051 kg

A car moving at 36 m/s passes a stationary police car whose siren has a frequency of 500 hz. What is the change in the frequency (in Hz) heard by an observer in the moving car as he passes the police car? (The speed of sound in air is 343 m/s.) Question options: 1) 416 2) 208 3) 105 4) 52 5) 552

3) 105

An organ pipe open at both ends is 1.5 m long. A second organ pipe that is closed at one end and open at the other is 0.75 m long. The speed of sound in the room is 330 m/s. Which of the following sets of frequencies consists of frequencies which can be produced by both pipes? Question options: 1) 110 Hz, 220 Hz, 330 Hz 2) 220 Hz, 440 Hz, 660 Hz 3) 110 Hz, 330 Hz, 550 Hz 4) 330 Hz, 440 Hz, 550 Hz 5) 220 Hz, 660 Hz, 1100 Hz

3) 110 Hz, 330 Hz, 550 Hz

The speed of a 10-kHz sound wave in seawater is approximately 1500 m/s. What is its wavelength in sea water? Question options: 1) 5.0 cm 2) 10 cm 3) 15 cm 4) 20 cm 5) 29 cm

3) 15 cm

A string is stretched and fixed at both ends, 200 cm apart. If the density of the string is 0.015 g/cm, and its tension is 600 N, what is the fundamental frequency? Question options: 1) 316 Hz 2) 632 Hz 3) 158 Hz 4) 215 Hz 5) 79 Hz

3) 158 Hz

A stretched string is observed to vibrate in three equal segments when driven by a 480 Hz oscillator. What is the fundamental frequency of vibration for this string? Question options: 1) 480 Hz 2) 320 Hz 3) 160 Hz 4) 640 Hz 5) 240 Hz

3) 160 Hz

By what factor will an intensity change when the corresponding sound level increases by 3 dB? Question options: 1) 3 2) 0.5 3) 2 4) 4 5) 0.3

3) 2

Two strings are respectively 1.00 m and 2.00 m long. Which of the following wavelengths, in meters, could represent harmonics present on both strings? Question options: 1) 0.800, 0.670, 0.500 2) 1.33, 1.00, 0.500 3) 2.00, 1.00, 0.500 4) 2.00, 1.33, 1.00 5) 4.00, 2.00, 1.00

3) 2.00, 1.00, 0.500

Calculate the pressure amplitude (in N/m2) of a 500 Hz sound wave in helium if the displacement amplitude is equal to 5 ´ 10-8 m. (r = 0.179 kg/m3, v = 972 m/s.) Question options: 1) 3.5 ´ 10-2 2) 1.6 ´ 10-2 3) 2.7 ´ 10-2 4) 4.2 ´ 10-2 5) 2.0 ´ 10-2

3) 2.7 ´ 10-2

The Young's modulus for aluminum is 7.02 ´ 1010 N/m2. If the speed of sound in aluminum is measured to be 5.10 km/s, find its density (in kg/m3). Question options: 1) 11.3 ´ 103 2) 7.80 ´ 103 3) 2.70 ´ 103 4) 29.3 ´ 103 5) 1.40 ´ 103

3) 2.70 ´ 103

If y = 0.02 sin (30x - 400t) (SI units), the frequency of the wave is Question options: 1) 30 Hz 2) 15/p Hz 3) 200/p Hz 4) 400 Hz 5) 800p Hz

3) 200/p Hz

A truck moving at 36 m/s passes a police car moving at 45 m/s in the opposite direction. If the frequency of the siren is 500 Hz relative to the police car, what is the change in frequency (in Hz) heard by an observer in the truck as the two vehicles pass each other? (The speed of sound in air is 343 m/s.) Question options: 1) 242 2) 238 3) 240 4) 236 5) 234

3) 240

A vertical tube one meter long is open at the top. It is filled with 75 cm of water. If the velocity of sound is 344 m/s, what will the fundamental resonant frequency be (in Hz)? Question options: 1) 3.4 2) 172 3) 344 4) 1.7 5) 688

3) 344

The variation in the pressure of helium gas, measured from its equilibrium value, is given by DP = 2.9 ´ 10-5 cos (6.2x - 3000t) where x and t have units m and s. Determine the speed (in m/s) of the wave. Question options: 1) 1515 2) 153 3) 484 4) 828 5) 101

3) 484

Bats can detect small objects such as insects that are of a size on the order of a wavelength. If bats emit a chirp at a frequency of 60 kHz and the speed of soundwaves in air is 330 m/s, what is the smallest size insect they can detect? Question options: 1) 1.5 mm 2) 3.5 mm 3) 5.5 mm 4) 7.5 mm 5) 9.8 mm

3) 5.5 mm

An earthquake emits both S-waves and P-waves which travel at different speeds through the Earth. A P-wave travels at 9000 m/s and an S-wave travels at 5000 m/s. If P-waves are received at a seismic station 1.00 minute before an S-wave arrives, how far away is the earthquake center? Question options: 1) 88.9 km 2) 1200 km 3) 675 km 4) 240 km 5) 480 km

3) 675 km

A clarinet behaves like a tube closed at one end. If its length is 1.0 m, and the velocity of sound is 344 m/s, what is its fundamental frequency (in Hz)? Question options: 1) 264 2) 140 3) 86 4) 440 5) 172

3) 86

Calculate the intensity level in dB of a sound wave that has an intensity of 15 ´ 10-4 W/m2. Question options: 1) 20 2) 200 3) 92 4) 9 5) 10

3) 92

A very long string is tied to a rigid wall at one end while the other end is attached to a simple harmonic oscillator. Which of the following can be changed by changing the frequency of the oscillator? Question options: 1) The speed of the waves traveling along the string. 2) The tension in the string. 3) The wavelength of the waves on the string. 4) All of the above. 5) None of the above.

3) The wavelength of the waves on the string.

A person standing in the street is unaware of a bird dropping that is falling from a point directly above him with increasing velocity. If the dropping were producing sound of a fixed frequency, as it approaches the person would hear the sound Question options: 1) drop in frequency. 2) stay at the same frequency. 3) increase in frequency. 4) decrease in loudness. 5) stay at the same loudness.

3) increase in frequency.

A student attaches a length of nylon fishing line to a fence post. She stretches it out and shakes the end of the rope in her hand back and forth to produce waves on the line. The most efficient way for her to increase the wavelength is to Question options: 1) increase the tension on the hose and shake the end more times per second. 2) decrease the tension on the hose and shake the end more times per second. 3) increase the tension on the hose and shake the end fewer times per second. 4) decrease the tension on the hose and shake the end fewer times per second. 5) keep the tension and frequency the same but increase the length of the hose.

3) increase the tension on the hose and shake the end fewer times per second.

A wave generated in a medium is a longitudinal wave when Question options: 1) there is a net transport of matter by the wave. 2) the molecules of the medium are unable to exert forces on each other. 3) molecular displacements are parallel to the wave velocity. 4) molecular displacements are perpendicular to the wave velocity. 5) the density of the medium is less than the density of water.

3) molecular displacements are parallel to the wave velocity.

To decrease the intensity of the sound you are hearing from your speaker system by a factor of 36, you can Question options: 1) reduce the amplitude by a factor of 12 and increase your distance from the speaker by a factor of 3. 2) reduce the amplitude by a factor of 4 and increase your distance from the speaker by a factor of 3. 3) reduce the amplitude by a factor of 2 and increase your distance from the speaker by a factor of 3. 4) reduce the amplitude by a factor of 3 and increase your distance from the speaker by a factor of 4. 5) reduce the amplitude by a factor of 3 and increase your distance from the speaker by a factor of 12.

3) reduce the amplitude by a factor of 2 and increase your distance from the speaker by a factor of 3.

While you are sounding a tone on a toy whistle, you notice a friend running toward you. If you want her to hear the same frequency that you hear even though she is approaching, you must Question options: 1) stay put. 2) run towards her at the same speed. 3) run away from her at the same speed. 4) stay put and play a note of higher frequency. 5) run towards her and play a note of higher frequency.

3) run away from her at the same speed.

Drummers like to have high-pitched cymbals that vibrate at high frequencies. To obtain the highest frequencies, a cymbal of a fixed size should be made of a material Question options: 1) with a low Young's modulus and a low density. 2) with a low Young's modulus and a high density. 3) with a high Young's modulus and a low density. 4) with a high Young's modulus and a high density. 5) composed of a metal-plastic laminate.

3) with a high Young's modulus and a low density.

Which of the following wavelengths could NOT be present as a harmonic on a 2 m long string? Question options: 1) 4 m 2) 2 m 3) 1 m 4) 0.89 m 5) 0.5 m

4) 0.89 m

Which of the following wavelengths could NOT be present as a standing wave in a 2 m long organ pipe open at both ends? Question options: 1) 4 m 2) 2 m 3) 1 m 4) 0.89 m 5) 0.5 m

4) 0.89 m

Two harmonic waves traveling in opposite directions interfere to produce a standing wave described by y = 2 sin (px) cos (3pt) where x is in m and t is in s. What is the distance (in m) between the first two antinodes? Question options: 1) 8 2) 2 3) 4 4) 1 5) 0.5

4) 1

The variation in the pressure of helium gas, measured from its equilibrium value, is given by DP = 2.9 ´ 10-5 cos (6.2x - 3000t) where x and t have units m and s, and DP is measured in N/m2. Determine the wavelength (in m) of the wave. Question options: 1) 1500 2) 0.32 3) 477 4) 1.01 5) 0.50

4) 1.01

A stone is thrown into a quiet pool of water. With no fluid friction, the amplitude of the waves falls off with distance r from the impact point as Question options: 1) 1/r3 2) 1/r2 3) 1/r3/2 4) 1/r1/2 5) 1/r

4) 1/r1/2

A jet plane has a sound level of 150 dB. What is the intensity in W/m2? Question options: 1) 1 2) 100 3) 10 4) 1000 5) 10000

4) 1000

By what factor is the intensity of sound at a rock concert louder than that of a whisper when the two intensity levels are 120 dB and 20 dB respectively? Question options: 1) 1012 2) 108 3) 106 4) 1010 5) 1011

4) 1010

A point source emits sound waves with a power output of 100 watts. What is the sound level (in dB) at a distance of 10 m? Question options: 1) 139 2) 119 3) 129 4) 109 5) 10

4) 109

When two organ pipes open at both ends sound a perfect fifth, such as two notes with fundamental frequencies at 440 Hz and 660 Hz, both pipes produce overtones. Which choice below correctly describes overtones present in both pipes? Question options: 1) 440, 880 and 1320 Hz. 2) 660, 1320 and 1980 Hz. 3) 880, 1320 and 1760 Hz. 4) 1320, 2640 and 3960 Hz. 5) They have no overtones in common.

4) 1320, 2640 and 3960 Hz.

It is possible to hear an approaching train before you can see it by listening to the sound wave through the track. If the elastic modulus is 2.0 ´ 1011 N/m2 and the density of steel is 7.8 ´ 103 kg/m3, approximately how many times faster is the speed of sound in the track than in air? (vair » 340 m/s.) Question options: 1) 20 2) 5 3) 10 4) 15 5) 25

4) 15

A length of organ pipe is closed at one end. If the speed of sound is 344 m/s, what length of pipe (in cm) is needed to obtain a fundamental frequency of 50 Hz? Question options: 1) 28 2) 86 3) 344 4) 172 5) 688

4) 172

The velocity of sound in sea water is 1533 m/s. Find the bulk modulus (in N/m2) of sea water if its density is 1.025 ´ 103 kg/m3. Question options: 1) 2.6 ´ 109 2) 2.2 ´ 109 3) 2.0 ´ 109 4) 2.4 ´ 109 5) 2.8 ´ 109

4) 2.4 ´ 109

A truck moving at 36 m/s passes a police car moving at 45 m/s in the opposite direction. If the frequency of the siren is 500 Hz relative to the police car, what is the frequency heard by an observer in the truck after the police car passes the truck? (The speed of sound in air is 343 m/s.) Question options: 1) 361 2) 636 3) 393 4) 396 5) 383

4) 396

If y = 0.02 sin (30x - 400t) (SI units), the angular frequency of the wave is Question options: 1) 30 rad/s 2) 30/2p rad/s 3) 400/2p rad/s 4) 400 rad/s 5) 40/3 rad/s

4) 400 rad/s

A car approaches a stationary police car at 36 m/s. The frequency of the siren (relative to the police car) is 500 Hz. What is the frequency (in Hz) heard by an observer in the moving car as he approaches the police car? (Assume the velocity of sound in air is 343 m/s.) Question options: 1) 220 2) 448 3) 5264 4) 552 5) 383

4) 552

The wavelength of light visible to the human eye is on the order of 5 ´ 10-7 m. If the speed of light in air is 3 ´ 108 m/s, find the frequency of the lightwave. Question options: 1) 3 ´ 107 Hz 2) 4 ´ 109 Hz 3) 5 ´ 1011 Hz 4) 6 ´ 1014 Hz 5) 4 ´ 1015 Hz

4) 6 ´ 1014 Hz

You are holding on to one end of a long string that is fastened to a rigid steel light pole. After producing a wave pulse that was 5 mm high and 4 cm wide, you want to produce a pulse that is 6 cm wide and 7 mm high. You must move your hand up and down once, Question options: 1) the same distance up as before, but take a shorter time. 2) the same distance up as before, but take a longer time. 3) a smaller distance up, but take a shorter time. 4) a greater distance up, but take a longer time. 5) a greater distance up, but take the same time.

4) a greater distance up, but take a longer time.

Superposition of waves can occur Question options: 1) in transverse waves. 2) in longitudinal waves. 3) in sinusoidal waves. 4) in all of the above. 5) only in (a) and (c) above.

4) in all of the above.

The fundamental frequency of a above middle C on the piano is 440 Hz. This is the tenor high A, but a convenient note in the mid-range of women's voices. When we calculate the wavelength, we find that it is Question options: 1) much shorter than the length of either a man's or woman's lips. 2) shorter than the length of a man's lips, but about the length of a woman's lips. 3) longer than a woman's lips, but about the length of a man's lips. 4) much longer than the length of either a man's or a woman's lips. 5) about the same length as either a man's or woman's lips.

4) much longer than the length of either a man's or a woman's lips.