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Exam 14: Waves and Sound

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Question 1

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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/m². Another student is 4.0 m away from the talkers. What sound intensity does the other student measure?

A) 6.2 × 10^-8 W/m²
B) 1.5 × 10^-7 W/m²
C) 8.3 × 10^-8 W/m²
D) 7.8 × 10^-7 W/m²
E) 2.5 × 10^-8 W/m²

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Question 2

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An elephant can hear sound with a frequency of 15.0 Hz. What is the wavelength of this wave? The speed of sound in air is 343 m/s.

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Question 3

Multiple Choice

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Two strings are made of the same material. String 1 has radius r₁ while string 2 has radius r₂ = r₁/2. When stretched by the same tension, the respective speed of propagation of waves v₁ and v₂ satisfy the condition

A car horn emits a frequency of 400 Hz. A car traveling at 20.0 m/s sounds the horn as it approaches a stationary pedestrian. What frequency does the pedestrian hear? The speed of sound in air is 343 m/s.

An open pipe of length L is resonating at its fundamental frequency. Which statement is correct?

The wave speed in an aluminum wire with a radius of 1.00 mm is 120 m/s. What is the tension in the wire? The density of aluminum is 2.70 × 10³ kg/m³.

FIGURE 14-1 -In Figure 14-1, the frequency is

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.

Two strings of identical mass per unit length are stretched with the same tension with their ends fixed, but one string is 0.33 cm longer than the other. Waves on these strings propagate at 34.0 m/s. The fundamental frequency of the shorter string is 258 Hz. What is the beat frequency when each string is vibrating at its fundamental frequency?

A uniform rope hangs from a ceiling. Without tugging on the rope, you give the bottom of the rope a wiggle and a wave travels upward along the rope. What can you say about the speed of the wave as the wave travels up the rope?

One of the harmonics of a string fixed at both ends has a frequency of 52.2 Hz and the next higher harmonic has a frequency of 60.9 Hz. What is the fundamental frequency of the string?

One of the harmonics of a column of air open at both ends has a frequency of 448 Hz and the next higher harmonic has a frequency of 576 Hz. What is the fundamental frequency of the air column?

A car horn emits a frequency of 400 Hz. A car traveling at 20.0 m/s sounds the horn as it goes away from a stationary pedestrian. What frequency does the pedestrian hear? The speed of sound in air is 343 m/s.

Four waves are described by the following expressions, 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?

A 6.00-m length of rope has a mass of 700 g. It is pulled taught with a force of 100 N. What is the speed of waves on the rope?

In the open ocean, the tides are waves that have a period of 12 hours and a speed of 750 km/hr. What is their wavelength?

A sound source approaches a stationary observer. The frequency heard by the observer is

The sound of 40 decibels is

FIGURE 14-1 -In Figure 14-1, the wavelength is

One of the harmonics of a column of air open at one end and closed at the other has a frequency of 448 Hz and the next higher harmonic has a frequency of 576 Hz. How long is the air column? The speed of sound in air is 343 m/s.