18. Waves &amp; Sound

A sound wave is emitted at a frequency of 300 Hz in air at a 0°C. As the sound wave travels through the air, the temperature increases. What is the wavelength of the sound wave at the following temperatures?

a. 0°C
b. 20°C
c. 45°C

The speed of sound in a certain monatomic gas is

320 m/s

at room temperature (

20 ℃

Which of the following expressions describes a wave with an amplitude of 10 cm, a wavelength of 31 cm, and a frequency of 22 Hz?

162

What are the longest and shortest wavelengths of sound that can be heard by a bat in air where the speed of sound is

343 m/s

275

A metal bar has a length of 1.5 m and a density of 6400 kg/m³. Sound waves take 3.9 × 10^-4 s to travel along the length of the bar. What is Young's modulus for this metal?

139

rank

What must be the stress (F/A) in a stretched wire of a material whose Young's modulus is Y for the speed of longitudinal waves to equal 30 times the speed of transverse waves?

339

Consider a sound wave in air that has displacement amplitude 0.0200 mm. Calculate the pressure amplitude for frequencies of (a) 150 Hz; (b) 1500 Hz; (c) 15,000 Hz. In each case compare the result to the pain threshold, which is 30 Pa

526

An oscillator vibrating at 1250 Hz produces a sound wave that travels through an ideal gas at 325 m>s when the gas temperature is 22.0°C. For a certain experiment, you need to have the same oscillator produce sound of wavelength 28.5 cm in this gas. What should the gas temperature be to achieve this wavelength?

277

One cue your hearing system uses to localize a sound (i.e., to tell where a sound is coming from) is the slight difference in the arrival times of the sound at your ears. Your ears are spaced approximately 20 cm apart. Consider a sound source 5.0 m from the center of your head along a line 45° to your right. What is the difference in arrival times? Give your answer in microseconds. Hint: You are looking for the difference between two numbers that are nearly the same. What does this near equality imply about the necessary precision during intermediate stages of the calculation?

225

(I) Calculate the speed of longitudinal waves in

(b) granite, using Tables in Chapters 12 and 13.

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(II) A sailor strikes the side of his ship just below the surface of the sea. He hears the echo of the wave reflected from the ocean floor directly below 2.4 s later. How deep is the ocean at this point? (Use Tables 12–1 and 13–1.)

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Two solid rods have the same bulk modulus but one is 2.1 times as dense as the other. In which rod will the speed of longitudinal waves be greater, and by what factor?

A motion sensor can accurately measure the distance d to an object repeatedly via the sonar technique used in Example 16–2. A short ultrasonic pulse is emitted and reflects from any objects it encounters, creating echo pulses upon their arrival back at the sensor. The sensor measures the time interval t between the emission of the original pulse and the arrival of the first echo.

(b) To measure an object’s speed the motion sensor makes 15 distance measurements every second (that is, it emits 15 sound pulses per second at evenly spaced time intervals), the measurement of t must be completed within the time interval between the emissions of successive pulses. What is the largest distance (at 20°C) that can be measured with the motion sensor?