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Chapter 16 Homework The Speed of Sound Qu. 1 A submerged scuba diver hears the sound of a boat horn directly above them on the surface of the lake. At the same time a friend on dry land 22m from the boat also hears the horn. The horn is 1.2m above the surface of the water. How far vertically is the scuba diver from the horn? (Ans: 90.8 m ) Bulk Modulus Qu. 2 A major earthquake centered on Loma Prieta, California, near San Francisco, occurred at 0h 4m 15s UTC on October 17, 1989. The primary seismic (P) waves from such an earthquake are longitudinal waves that travel through the earth’s crust. The P waves were detected at Caracas, Venezuela, at 0h 13m 54 UTC after having traveled a distance of 6280 km. The average density of the earth’s crust is 3.3 g/cm3. Use this value to calculate the bulk modulus of the earth’s crust along the path traveled by the P waves. ( Ans: 3.8 x 1011 Pa). Pressure Amplitude and Displacement Amplitude Qu. 3 Sound waves in air with a frequency of 1000 Hz and a displacement amplitude of 1.2 x 10-8 m produce a pressure amplitude of 3 x 10-2 Pa. a) What is the wavelength of these sound waves given the speed of sound in air is 344 m/s? ( Ans: 0.34 m) b) For 1000 Hz waves in air, what displacement amplitude would be needed for the pressure amplitude to be at the pain threshold, which is 30 Pa? (Ans: 1.2 x 10-5 m) c) For what wavelength and frequency will waves with a displacement amplitude of 1.2 x 10-8 m produce a pressure amplitude of 1.5 x 10-3 Pa. (Ans: 6.8 m, 50.5 Hz)