ism_chapter_15

ism_chapter_15 - Chapter 15 Wave Motion Conceptual Problems...

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1145 Chapter 15 Wave Motion Conceptual Problems *1 Determine the Concept The speed of a transverse wave on a rope is given by µ F v = where F is the tension in the rope and is its linear density. The waves on the rope move faster as they move up because the tension increases due to the weight of the rope below. 2 Determine the Concept The distance between successive crests is one wavelength and the time between successive crests is the period of the wave motion. Thus, T = 0.2 s and f = 1/ T = 5 Hz. correct. is ) ( b 3 Picture the Problem True. The energy per unit volume (the average energy density) is given by 2 0 2 2 1 av s ρω η = where s 0 is the displacement amplitude. 4 Determine the Concept At every point along the rope the wavelength, speed, and frequency of the wave are related by . f v = λ The speed of the wave, in turn, is given by F v = where F is the tension in the rope and is its linear density. Due to the weight of the rope below, the tension is greater at the top and the speed of the wave is also greater at the top. Because v, the wavelength is greater at the top. *5 Determine the Concept The speed of the wave v on the bullwhip varies with the tension F in the whip and its linear density according to F v = . As the whip tapers, the wave speed in the tapered end increases due to the decrease in the mass density, so the wave travels faster. 6 Picture the Problem The intensity level of a sound wave β , measured in decibels, is given by () 0 log dB 10 I I = where I 0 = 10 -12 W/m 2 is defined to be the threshold of hearing. Express the intensity of the 60-dB sound: 0 60 log dB 10 dB 60 I I = 0 6 60 10 I I =
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Chapter 15 1146 Express the intensity of the 30-dB sound: () 0 30 log dB 10 dB 30 I I = 0 3 30 10 I I = Because I 60 = 10 3 I 30 : false. is statement The 7 Determine the Concept No. Because the source and receiver are at rest relative to each other, there is no relative motion of the source and receiver and there will be no Doppler shift in frequency. 8 Determine the Concept Because there is no relative motion of the source and receiver, there will be no Doppler shift and the observer will hear sound of frequency f 0 . correct. is ) ( a *9 •• Determine the Concept The light from the companion star will be shifted about its mean frequency periodically due to the relative approach to and recession from the earth of the companion star as it revolves about the black hole. 10 Determine the Concept In any medium, the wavelength, frequency, and speed of a wave are related through λ = v / f . Because the frequency of a wave is determined by its source and is independent of the nature of the medium, if v differs in the two media, the wavelengths will also differ. In this situation, the frequencies are the same but the speeds of propagation are different.
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ism_chapter_15 - Chapter 15 Wave Motion Conceptual Problems...

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