91影视

Find the ratios (greater to smaller) of the (a) intensities, (b) pressure amplitudes, and (c) particle displacement amplitudes for two sounds whose sound levels differ by $\mathbf{37}\mathbf{\text{鈥塪叠}}$.

In Fig. 17-45, sound waves$\mathbf{A}$and$\mathbf{B}$, both of wavelength$\mathbf{位}$, are initially in phase and traveling rightward, as indicated by the two rays. Wave Ais reflected from four surfaces but ends up traveling in its original direction. What multiple of wavelength$\mathbf{位}$is the smallest value of distance$\mathbf{L}$in the figure that puts Aand Bexactly out of phase with each other after the reflections?

A trumpet player on a moving railroad flatcar moves toward a second trumpet player standing alongside the track while both play a $\mathbf{440}\mathbf{\text{鈥塇锄}}$note. The sound waves heard by a stationary observer between the two players have a beat frequency of$\mathbf{4.0}\mathbf{\text{鈥塨别补迟蝉}}\mathbf{/}\mathbf{\text{s}}$.What is the flatcar鈥檚 speed?

In Fig. 17-46, sound of wavelength $\mathbf{0}\mathbf{.850}\mathbf{\text{鈥尘}}$is emitted isotropically by point source S. Sound ray 1 extends directly to detector D, at distance $\mathit{L}\mathbf{}\mathbf{=}\mathbf{10.0}\mathbf{\text{鈥尘}}$. Sound ray 2 extends to Dvia a reflection (effectively, a 鈥渂ouncing鈥�) of the sound at a flat surface. That reflection occurs on a perpendicular bisector to the SDline,at distance dfrom the line. Assume that the reflection shifts the sound wave by$\mathbf{0}\mathbf{.500}\mathbf{位}$. For what least value of d(other than zero) do the direct sound and the reflected sound arrive at D(a) exactly out of phase and (b) exactly in phase?

Question: A stone is dropped into a well. The splash is heard 3.00s later. What is the depth of the well?

Question: Figure 17-28 shows a moving sound source S that emits at a certain

frequency, and four stationary sound detectors. Rank the detectors

according to the frequency of the sound they detect from the

source, greatest first.

A detector initially moves at constant velocity directly toward a stationary sound source and then (after passing it) directly from it. The emitted frequency is $\mathit{f}$. During the approach the detected frequency is${\mathit{f}}_{\mathbf{a}\mathbf{p}\mathbf{p}}^{\mathbf{\text{'}}}$ and during the recession it is${\mathbf{f}}_{\mathbf{rec}}^{\mathbf{\text{'}}}$ . If the frequencies are related by $\mathbf{(}{\mathbf{f}}_{\mathbf{app}}^{\mathbf{\text{'}}}\mathbf{鈭�}{\mathbf{f}}_{\mathbf{rec}}^{\mathbf{\text{'}}}\mathbf{)}\mathbf{/}\mathbf{f}\mathbf{}\mathbf{=}\mathbf{0.500}$, what is the ratio ${\mathbf{v}}_{\mathbf{D}}\mathbf{/}\mathbf{v}$of the speed of the detector to the speed of sound?

(a) If two sound waves, one in air and one in (fresh) water, are equal in intensity and angular frequency, what is the ratio of the pressure amplitude of the wave in water to that of the wave in air? Assume the water and the air are at $\mathbf{20}\mathbf{掳}\mathbf{C}$. (See Table 14-1.)

(b) If the pressure amplitudes are equal instead, what is the ratio of the intensities of the waves?

A continuous sinusoidal longitudinal wave is sent along a very long coiled spring from an attached oscillating source. The wave travels in the negative direction of an xaxis; the source frequency is$\mathbf{25}\mathbf{\text{鈥塇锄}}$; at any instant the distance between successive points of maximum expansion in the spring is; the maximum longitudinal displacement of a spring particle is$\mathbf{24}\mathbf{\text{鈥塩尘}}$; and the particle at$\mathbf{x}\mathbf{}\mathbf{=}\mathbf{}\mathbf{0}$has zero displacement at time$\mathbf{t}\mathbf{}\mathbf{=}\mathbf{}\mathbf{0}$. If the wave is written in the form$\mathbf{s}\mathbf{(}\mathbf{x}\mathbf{,}\mathbf{}\mathbf{t}\mathbf{)}\mathbf{}\mathbf{=}{\mathbf{s}}_{\mathbf{m}}\mathbf{cos}\mathbf{(}\mathbf{kx}\mathbf{卤}\mathbf{}\mathbf{蝇迟}\mathbf{)}$, what are (a)${\mathbf{s}}_{\mathbf{m}}$, (b)$\mathbf{k}$, (c)$\mathbf{蝇}$, (d) the wave speed, and (e) the correct choice of sign in front of$\mathbf{蝇}$?

Ultrasound, which consists of sound waves with frequencies above the human audible range, can be used to produce an image of the interior of a human body. Moreover, ultrasound can be used to measure the speed of the blood in the body; it does so by comparing the frequency of the ultrasound sent into the body with the frequency of the ultrasound reflected back to the body鈥檚 surface by the blood. As the blood pulses, this detected frequency varies.

Suppose that an ultrasound image of the arm of a patient shows an artery that is angled at$\mathbf{胃}\mathbf{}\mathbf{=}\mathbf{20}\mathbf{掳}$to the ultrasound鈥檚 line of travel (Fig. 17-47). Suppose also that the frequency of the ultrasound reflected by the blood in the artery is increased by a maximum of$\mathbf{5495}\mathbf{\text{鈥塇锄}}\mathbf{}$from the original ultrasound frequency of$\mathbf{5.000}\mathbf{}\mathbf{000}\mathbf{\text{鈥塎贬锄}}$

(a) In Fig. 17-47, is the direction of the blood flow rightward or leftward?

(b) The speed of sound in the human arm is$\mathbf{1540}\mathbf{\text{鈥尘}}\mathbf{/}\mathbf{\text{s}}$. What is the maximum speed of the blood?

(c) If angleuwere greater, would the reflected frequency be greater or less?