Chapter 12: Q65P (page 328)
(I) The wake of a speedboat is 12° in a lake where the speed of the water wave is 2.2 km/h. What is the speed of the boat?
The speed of the boat is \(10.58\;{\rm{km/h}}\).
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Question: The “alpenhorn” (Fig. 12–42) was once used to send signals from one Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were used to create deep sounds. When played as a musical instrument, the alpenhorn must be blown in such a way that only one of the overtones is resonating. The most popular alpenhorn is about \({\bf{3}}{\bf{.4}}\,{\bf{m}}\) long, and it is called the \({{\bf{F}}^{\bf{\# }}}\) horn. What is the fundamental frequency of this horn, and which overtone is close to\({{\bf{F}}^{\bf{\# }}}\)? (See Table12–3.) Model as a tube open at both ends.
To make a given sound seem twice as loud, how should a musician change the intensity of the sound?
(a) Double the intensity.
(b) Halve the intensity.
(c) Quadruple the intensity.
(d) Quarter the intensity.
(e) Increase the intensity by a factor of 10.
The sound level near a noisy air conditioner is 70 dB. If two such units operate side by side, the sound level near them would be
(a) 70 dB.
(b) 73 dB.
(c) 105 dB.
(d) 140 dB.
Consider the two waves shown in Fig. 12–31. Each wave can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two component frequencies farther apart? Explain.
What is the intensity of a sound at the pain level of 120 dB? Compare it to that of a whisper at 20 dB.
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