18. Waves & Sound

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?

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?

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?

Calculate the speed of longitudinal waves in granite, using Tables in Chapters 12 and 13.

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.)

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.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?

P and S waves from an earthquake travel at different speeds, and this difference helps locate the earthquake “epicenter” (where the slippage took place). Assuming typical speeds of 8.5 km/s and 5.5 km/s for P and S waves, respectively, how far away did the earthquake occur if a particular seismic station detects the arrival of these two types of waves 1.5 min apart?

What is the speed of sound in air (a) on a cold winter day in Minnesota when the temperature is -25°F, and (b) on a hot summer day in Death Valley when the temperature is 125°F?

A metal bar with a length of 1.50 m has density 6400 kg/m³. Longitudinal sound waves take 3.90 × 10^-4 s to travel from one end of the bar to the other. What is Young's modulus for this metal?

(II) Determine the wavelength of a 6200-Hz longitudinal wave traveling along an iron rod. Use Tables 12–1 and 13–1.

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. Assume that during a lab period the room’s temperature increases from 20°C to 23°C. What percent error will this introduce into the motion sensor’s distance measurements?

A 15-cm-long aluminum tank is filled with ethyl alcohol. A high-frequency ultrasound wave travels horizontally through one wall of the tank and then through the alcohol. There are 275 times more cycles of the wave in the alcohol than in the aluminum wall. How thick is the wall of the tank?