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Ch apter 11 - Answer to Problems 3 ,13, 21 , 25 , 49 3. The intensity of the sound wave from a jet airplane as it is taking off is 1.0 2 W/m 2 at a distance of 5.0 m. What is the intensity of the sound wave that reaches the ears of a person standing at a d istance of 120 m from the runway? Assume that the sound wave radiates from the airplane equally in all directions. Answer: The intensity of the sound as a function of the distance is given by I 2 /I 1 = (P/4pr 2 2 ) / (P/4pr 1 2 ) = r 1 2 /r 2 2 I 2 = I 1 x(r 1 2 /r 2 2 ) = (1.0x10 2 W/m 2 )x(5.0m/120m) 2 =170 x10 -3 W /m 2 13. What is the wavelength of a wave whose speed and period are 75.0m/s and 5.00ms respectively Given: v=75.0m/s ; T=5.00msQuestion: ? 21. . A wave on a string has equation y ( x, t ) = (4.0 mm) sin ( t kx ) where = 6.0 2 rad/s and k = 6.0 rad/m. (a) What is the amplitude of the wave? (b) What is the wavelength? (c) What is t he period? (d) What is the wave speed? (e) In which direction does the wave travel?

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• Fall '09
• HUANG
• Hertz, Wavelength, sound wave

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