What is the evidence thazkpdygsv464 z-ef5 f8mqc*e 4t sound travels as a wave?

What is the evidence that sound is a form op88vb *n hlspyvg /9l(2 n(*jkzbhlk(f energy?

Children sometimes play with a homemade “te urppgvg+i*49 b-+o3xh hgk: alephone” by attaching a string to the bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. pb* 9+xukrpghv:-+3ghiao 4g 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air i7svwj.on pm- rjgqv8d.q kq3l.1 5x ,pnto water, do you expect the frequency or wavelexv q1 p-5g.plmj q7,s3d8vrq.w. j oknngth to change?

What evidence can you give that the speed of sound in air does not depezj) m72ndu;y gnd significantly on frequ;72u nm) yjzgdency?

The voice of a person woy v1od3 j e4 7qj4mbv6lw2i:cho has inhaled helium sounds very high-pitched. Why?

How will the air temperature in a room affect the pitcd:;blk p flfs6nc-5e: w1rw4una b5v1h of organ pipes?

Explain how a tube might be used as a fil1 r336h q9e0.lgcx te+0pqigf t.efa zter to reduce the amplitude of sounds in various frequency ranges. (An example is a car muffleg19+ea3i.ef6ep xf00 3.lcgqrqtzthr.)

Why are the frets on a guitar (Fi ch*7( t*gcec i2e urze7d1u)mg. 12–30) spaced closer together as you move up the fingerboard toward the bri71e(t eccz u **r7ciue2hmgd )dge?

A noisy truck approaches you from behind a builo,ya s0qxc 4k1ding. Initially you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Sectio4c0xs1 kq o,ayn 11–15 on diffraction.]

Standing waves can be said to be due to “i4 ,c:bm,up9:fceyfxk6 , 0qqulbcp *qnterference in space,” whereas beats can be said to be due tcl 4efckfc,,*p:0: y6 q,m xuqq9bbupo “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers9g0 pqebo5mp8ai (hii:my1r9 were lowered, would the points D and C (where destructive and constructive interference occur) move farther apart or closer to hma5p:i190o (9qmgi8 ebiyprgether?

Traditional methods of prv9w f h:hnk* xv00mbi9otecting the hearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technology, headphones are wo: hhi9v0mv*nwf 9bxk0rn that do not block the ambient noise. Instead, a device is used which detects the noise, inverts it electronically, then feeds it to the headphones in addition to the ambient noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. c9ourq/7/ r*.u rg-ey3b nu zmEach 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 *er 7rcu3r/gy bq-n/u9 . ozumfrequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if nf;g2p)/pqv* 8 je xbqthe source and observer move in the same direction, with the same velocity?vxq j;2gbe8qn pf p)*/ Explain.

If a wind is blowing, will this alter the frequency of the sound hea h(y.k 2 ta7;iajnm:rwrkl ,t7rd by a person at rest with respect to the source? Is the wavelength or veloci.kyi na2h:tl7 m,r;r(jat7 k wty changed?

Figure 12–32 shows various positions of a child in mot1be5j ,y(mvta1r b gc:ion on a swing. A monitor is blowing a whistle in front of the child on the ground. At which position, A through E, will the child ybbg:51 cjv 1ae(,mrthear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length ofpqz(h7 q)nl40aa ki(yfam7 h ; a lake by listening for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the length of the lk ;my)7h0q(haaz(7 f ip4naqlake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterliy 6 lbfaq+pnf;+5yu/sne. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s lateyn+l sya;f+qfp 65/ub r. How deep is the ocean at this point? Assume the speed of sound in seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air 97suj;o(kztrwf r/u(at 20 $^{\circ} $ C for sounds in the maximum range of human hearing, 20 Hz to 20,000 Hz. $\lambda_{20Hz}$ =    m $\lambda_{20kHz}$ =    $ \times10^{-2 }$ m(b) What is the wavelength of a 10-MHz ultrasonic wave?    $ \times10^{ -5}$m

  An ocean fishing boat is3dzp5lxn u,2hw :t5hl drifting just above a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 1p: udl5 whh 5zn,23ltx2–33). How much time elapses before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cli eu9wzrcip-67 bst1c8ff. The splash it makes when striking the water below is heard 3.5 s la79w e 618bucic- ztprster. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the cotm8 9l v20)gmwtegaw :ncrete pavement. Aea)mw g t2wgm8l9v0 t: moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 1.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of ctc8rllvy85 b5 hz* n3distance by the “5-second rule” for estimat y zncc35b5rh88l lvt*ing the distance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a so/ wi v2*6 i.pbyad-epxihze3)und at the pain level of 120 dB?    W/$m^2$Compare it to that of a whisper at 20 dB.    $ \times10^{-10 }$W/$m^2$

  What is the sound level of a sound whose iek ntd *wa/gge,1 w- kn*f8s:kntensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB whkt-b +leg8;ym5v cie9en fired simultaneously at a certain place, what will be the sound level if only one k8-ic9bg+et m ylev5;is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equally noisyw//co6 qa9qi5 5jsjp+w/zsna jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person expe q+ oa j5c nwz9i/pa/5/6qwjssrience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a sihs1.4q2*h,acwt r j zykw.mf2pff.2 ggnal-to-noise ratio of 58 dB, whereas for a CD playek.w fpqjtz1hwh2yff 24. 2m.sacg *,rr it is 95 dB. What is the ratio of intensities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of s3f+uet bx 2.djpz/f.lound from a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly/j3tpe+f 2.fl zubd .x uniformly over a sphere centered on the mouth. $\approx$    $ \times10^{ -6}$W(Round to the nearest integer)
(b) How many people would it take to produce a total sound output of 100 W of ordinary conversation? [Hint: Add intensities, not dB’s.]$\approx$    $ \times10^{7}$people

  A 50-dB sound wave s26 rmdejn0-mk trikes an eardrum whose area is $5 \times10^{ -5} m^2$ (a) How much energy is absorbed by the eardrum per second?    $ \times10^{-12}$W (b) At this rate, how long would it take your eardrum to receive a total energy of 1.0 J?   $ \times10^{ 3}$yr

  Expensive amplifier A is rated at 250to c+4w.e vtgci j9 .-t937 nj)ufcczt W, while the more modest amplifier B is rated at 40 W. (a)vfgw7z4itj+coc 9ut.tt. j-9ec 3)cn Estimate the sound level in decibels you would expect at a point 3.5 m from a loudspeaker connected in turn to each amp.$I_{250}$ =    dB $I_{40}$ =    dB (b) Will the expensive amp sound twice as loud as the cheaper one?

  At a rock concert, a dB meter registered 130 dB when placed 2.8 k i- 7sr.*ftduo sn7,xm in front of a loudspeaker on thetko,r-xfsu77.*ni s d stage.
(a) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?$\approx$    $ \times10^{2 }$W(“Round to one decimal place)
(b) How far away would the sound level be a somewhat reasonable 90 dB?   $ \times10^{2}$m

  Human beings can typically detect a difference in sound level of 2.0 dB. What islns/71tky c+1kspvd*ew 8h/7r zr)b u the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: sz/ ur yw7 1)t*vpdehrc18 l+ns7kbk/See Section 11–9.]$\approx$   

  If the amplitude of a sochza2 u n42 s3dsls+9zund wave is tripled, (a) by what factor will the intensity increase?al4z3dsu2h+nc 9 zs2 s Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one 8e 5s(w,mc3okqty3 ads hz,7phas twice the frequency of the other. Ws7 ohmya 3ts5eq(8 pk,,zc3dwhat is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wavuj94bwi,ux6voc ;w z6 e in air that corresponds to a displacement amplitu u;v, o6j9w4bc uiw6zxde of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must h -+1ttx 6q4nxpnxzzfri0 s i*+ave what sound level to seem as loud as a 100-Hz tone that has a 50-dB sound level*t+xntn 6 qixpzfz- 0ix +1rs4? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect whzk)k.z ei0eht 29ys8;2ii/s cg bmv4ien the souns iy c zbi)28 ti.94z/e2hi0;mskvgekd level is 30 dB? (See Fig. 12–6.)

  Your auditory system can a3lt9 aic, c/ywz7l1lk ccommodate a huge range of sound levels. What is the ratio of highest to lowest intensity at 1w3/ ikl,c 7tzlal9 yc
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has *9 lq;ufka4ye vx f .u*p0i:vm5mfu9mp: cfb+ a fundamental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Undefbmv.; u+m* vffeqpcm l0y4fu:5u :xip*ak9 9r what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are*wlh -xw ,ao.w the fundamental and first three audible overtones if t,hawlo*.-w w xhe pipe is
(a) closed at one end, $f_{1}$ =    Hz $f_{3}$ =    Hz $f_{5}$ =    Hz $f_{7}$ =    Hz
(b) open at both ends?$f_{1}$ =    Hz $f_{2}$ =    Hz $f_{3}$ =    Hz $f_{4}$ =    Hz

  (a) What resonant frequency would you expect from blowing across the top of0dw)xn4p) pt:ruo bv. an empty soda bottle that is 18 cm deep, if o4 xpr:n)t)0u bp.wvdyou assumed it was a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pa4ge02sv)i ) vxovoa(ipe organ with open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range ofe )0sa )g(xva 2oiv4ov the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its third harmon(w ihga igp +f9(tu(v)gt4i2*ilwsp)ic. What will be its fundamental fri+ psf u ig)glgv(pa 2*ti4tw9i (w)(hequency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.7,hd0,jef shbj, 8a x2i3 m long and is tuned to play E above middle C (330 Hzefb,0sh,j2d ji ,8xah).
(a) How far from the end of this string must the finger be placed to play A above middle C (440 Hz)?$\approx$    m
(b) What is the wavelength on the string of this 440-Hz wave? $\approx$    m
(c) What are the frequency and wavelength of the sound wave produced in air at 20°C by this fingered string?    Hz    m

  (a) Determine the length of an open organ pipe that e4y:7d8sy d9rawvry 1d2uuc0 tmits middle C (262 Hz) when the temperatv0yys d 18r4wrut aud 2:dc97yure is 21 $^{\circ} $ C.    m
(b) What are the wavelength and frequency of the fundamental standing wave in the tube?    Hz    m
(c) What are $\lambda$ and $f$in the traveling sound wave produced in the outside air?    Hz    m

  An organ is in tune at 20 r (hhd9m65u3(kr ccqt$^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Example 12–10 shouldkcqrbgi,f /p /v9s3v : the hole be that must be u:fbspq /k/3 ,c 9grivvncovered to play D above middle C at 294 Hz?    m

  (a) At T = 20 $^{\circ} $C how long must an open organ pipe be to have a fundamental frequency of 294 Hz?    m
(b) If this pipe is filled with helium, what is its fundamental frequency?   Hz

  A particular organ pipe can resonate at 264 Hz, 440 H zs:zykr7t*wohp5(v42ez) 5vh tre *xz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an opeyre5zp o :hsttk2z)v7vw5ex r*(4z h*n or a closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m long is open at both ends. It resonat(2k/yaj k lvxzraenq /13kc 8,es at two successive harmonics c8kkxa ,l z/ 1j2q(knayve 3/rof frequencies 275 Hz and 330 Hz. What is
(a) the fundamental frequency,    Hz
(b) the speed of sound in the gas in the tube?$\approx$    $ \times10^{2 }$ m/s

  A pipe in air at 20 u dendc (n2x) m) z3-rvuz*or8k0cwb0$^{\circ} $ C is to be designed to produce two successive harmonics at 240 Hz and 280 Hz. How long must the pipe be, and is it open or closed?  ----待选择----closedopen  f =    m

  How many overtones are pre: udw/0r pms4psent within the audible range for a 2.14-m-long organ pu /0 4mdrppws:ipe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It is open to the outsio2.mw(m 66eu xv*m vco/fq no0de and is closed am2c(6omx vf./mwueo60 *ovq nt the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves in the ear canal. What is the relationship of your answer to the information in the graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when trying toq9,s(yq9 sjrj adjust two strings, one of which is sounding 440 Hz. How far off in frequys9 ,qjj s9(qrency is the other string? ±    Hz

  What is the beat frequency if middle Ca(3drhdghn sy l,+ 5nus-k75 s (262 Hz) and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle operates at 23.5 kHz,;..jpqq0+f7k ogr; ds.ct xcv while another (brand X) operates at an unknown frequency. If neither whistle can be heard bp;cv0f ..gctj7kqqo dx;r s.+y humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produc, z,8d1bbmhchd e3w h-9 yd-ndes 4 beats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tem h,-hwd dh3-y8,nb9d cz1dbuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the samee 74g+jofh+cb.5dfcw7wp ,qv frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will 7++ hwcj.,d5wq4cbef7op vg f be the beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical w)1fg ( i.i /;lr,fli0*wziplxkuj8p flutes each try to play middle C (262 Hz), but one is at 5.0°C anpw wk/i(liz,x;. jfgf)0rl1i iu p8*ld the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and ,uk l(ao a zfl.b.p3/iC. Fork B has a frequency of 441 Hz; when A and B are sounded tuo.ab 3zk,f. a(p/il logether, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequencies are possible when A and C are sounded together?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apart. A person stands 3.00 m from one speae+ y+/nl-kt ynker and 3.50 m from tk +y+e lyn-tn/he other.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are supposed to be vibrating at 132 Hz, ba3y8i+ 843ap kneo+m+dae fsx ut a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must be tf8e4e+so+i axk3a8mn p+ dya 3he frequency of the other ?   Hz    Hz
(b) By how much (in percent) must the tension be increased or decreased to bring them in tune?   % increase    %decrease

  A source emits sound of wavelengths 2.64 m and 2.76 m in air. How many beat,j*ii i o2 ek8j6.h8lrmzybn;s per second will be heard? (Assume T = 20, irlj; iz byhk88ij.*n6moe 2 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequencyu+61 a n,surkx of a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a speed of 30 urxs6an +k u1,m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing sti e3)r kx3r; ,kpejp7avll. What frequency do you detect if a fire engine whose siren emits at 1550 Hz moves at a sperxr pk3jk)vp ;,7a3e eed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift vd s.aoj ,v:;j;opf:gin frequency if a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two freq.jo; pfjga sdo,::; vvuencies exactly the same? Are they close? $f'_{source\,movine}$    Hz
$f'_{observe\,movine}$    Hz
(b) Repeat the calculation for 150 m/s and then again
$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz
(c) for 300 m/s What can you conclude about the asymmetry of the Doppler formulas?$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz

  Two automobiles are equipped with the same single freqa4x5leka9seyf g 55h9uency horn. When one is at rest and the other is moving toxh9g9 5ele4fy55saak ward the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at f-/s kwjuxq :z/4xsz9ufc0 s ;50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is the received sound frequenc/ssxk/s;9 q4xc-: uj0zf uzwf y?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall az.jq:a1x *vvuurk :7jt a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz j:xvz1ar j:v7*uk. uq. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played(m6 ;ye zxxr0 8ruoiy- on a moving flat train car at a frequency of 75 Hz, and a second identical tuba pla y0m iz86rxr(uoe;-xyyed the same tone while at rest in the railway station. What beat frequency was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measyn)a-sgq3a.1moslu c9w0vt :y 05p wmure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 m/s What is the expected beat frequency if blood is flowing in large le:-m.c) lnaa0oyum 5wyp g0 sq31t9sw vg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of fre /2c hd0-mycjzh(ag e -xep 9ppet05p4n-dfh+ quency $2.25 \times10^{ 6}$Hz is used to monitor the heartbeat of a fetus. A (maximum) beat frequency of 500 Hz is observed. Assuming that the speed of sound in tissue is $1.54 \times10^{3 }$ m/s calculate the maximum velocity of the surface of the beating heart.    m/s

  A factory whistle emits soun4:wn8w c zil1ud of frequency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers hear who arnw1z84 wl ui:ce located, at rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object mov)zg+a/ , xltmb*cibn)ing on land if its speed at 20 $^{\circ} $C is Mach 0.33?    m/s
(b) A high-flying jet cruising at 3000 km/h displays a Mach number of 3.2 on a screen. What is the speed of sound at that altitude?    m/s

  An airplane travels at Mach 2.3 wherxzwi; 6*m6ze .6(3 vltqpymyxe the speed of sound is 310 m/s (a) What is the angle t6zw ;3ltv 6(xmyz.y epqmx6*ihe shock wave makes with the direction of the airplane’s motion?    $^{\circ} $
(b) If the plane is flying at a height of 7100 m, how long after it is directly overhead will a person on the ground hear the shock wave? $\approx$    s (Round to the nearest integer)

  A space probe enters the thin atmosd(/wn(yipa6 k+roff .e-b om-phere of a planet where the speed of sound is onlorbmapky6(dn/we.(+ f- i-ofy about 35 m/s
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $

  A meteorite traveling 8500 m/s strikes the ocean. Determine the shock wave angl) l5soey1 dxq-q*hj3 we it p*sqxqj-e y1w 3h5 l)doroduces
(a) in the air just before entering the ocean, $\approx$    (Round to the nearest integer)
(b) in the water just after entering.    $^{\circ} $
Assume T = 20 $^{\circ} $C

Show that the angle m j/p,o7bs mmwovy+o x.u+oek 8 429qi$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and see a plane exactly 1.5 km above thebt ;+kqwo1x 2p ground flying faster than the speed of sound. By the time you hear the so+2 tk owp;qbx1nic boom, the plane has traveled a horizontal distance of 2.0 km. See Fig. 12–34. Determine
(a) the angle of the shock cone, $\theta$    $^{\circ} $
(b) the speed of the plane (the Mach number). Assume the speed of sound is 330 m/s   

  A fish finder uses a sonar device that sends 20,000-*;s/tro j ubm-Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed to work is 200 m, whats m/b-r jt*o;u is the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are there in the human audible r8 bp(s q xni0*n:s-2 emwyrzg.ange? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display calle0q ezgf;3p,phd a sewer pipe symphony. It consists of many plastic pipes of varefp3 h 0,q;zpgious lengths, which are open on both ends.
(a) If the pipes have lengths of 3.0 m, 2.5 m, 2.0 m, 1.5 m and 1.0 m, what frequencies will be heard by a visitor’s ear placed near the ends of the pipes?
$f_{3.0}$ =    Hz
$f_{2.5}$ =    Hz
$f_{2.0}$ =    Hz
$f_{1.5}$ $\approx$    Hz (Round to the nearest integer)
$f_{1.0}$ $\approx$    Hz (Round to the nearest integer)
(b) Why does this display work better on a noisy day than on a quiet day?

  A single mosquito 5.0 m from a person ma;oz dr3:5 f*dwcei7rj oy 81zmkes a sound close to the threshold of human hearing1yec od3zd ;mow8r57fri :jz* (0 dB). What will be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB sound and an 87ozjbx hb;w4l ;tyo41 /-dB sound are heard simultan/1;oolb z;b hw 4yxj4teously?    dB

  The sound level 12.0 m from a loudspeaker, placit( mv sih61g2ed in the open, is 105 dB. What is the acoustic power output (W) om hg26vt(si i1f the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz. The p-zv , fsjm9n4qower output drops bvsz f -4nmqj9,y 10 dB at 15 kHz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices over their e3 v8cbvi p,yey: m;6tgars. Assume that the sound level of a jet airplane engine, at a distance of 30 m, is 140 dB, and that the average human ear has an effective radius of 2.0 cm. What would be the power intercepp: vi;bg evt3,6 myy8cted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications systems, the gain, w ab2u:ja;5mo y:7 kxp$\beta$ in decibels is defined as
$\beta$ = 10log($\frac{P_{out}}{P_{in}}$)
where $P_{in}$ is the power input to the system and $P_{out}$ is the power output. A particular stereo amplifier puts out 100 W of power for an input of 1 mW. What is its gain in dB?   dB

  Each string on a violin is tuned to a fr )/3lx6zk lo4 4jicopwequency 1$\frac{1}{2}$ times that of its neighbor. The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string?
$f_{A}$ =    $\mu_{A}$
$f_{B}$ =    $\mu_{A}$
$f_{C}$ =    $\mu_{A}$

  The A string of a violin is 32 cm long between fixed pointcznx iwuc w:(c-n.j :ruo+pkl)cj94 /(mx5rws with a fundamental frequency of 440 Hz and a m ccr+n-ckrw j( :u4:(xojzl9mwiu./ nxpw) c5ass per unit length of $6.1 \times10^{-4 }$ kg/m
(a) What are the wave speed and tension in the string?    $ \times10^{2 }$ m/s    N
(b) What is the length of the tube of a simple wind instrument (say, an organ pipe) closed at one end whose fundamental is also 440 Hz if the speed of sound is in air?    m
(c) What is the frequency of the first overtone of each instrument?   Hz    Hz

  A tuning fork is set into vibration above a verticalzxz)y39ow5y u open tube filled with water (Fig. 12–35). The water levyzoxy5 w)3uz9 el is allowed to drop slowly. As it does so, the air in the tube above the water level is heard to resonate with the tuning fork when the distance from the tube opening to the water level is 0.125 m and again at 0.395 m. What is the frequency of the tuning fork?   Hz

  A 75-cm-long guitar string of mass 2.10 g is nxvu v)ob y7.wqmxi+; 5ear a tube that is open at one end and also 75omxvb.;w7qiu yx+5 v ) cm long. How much tension should be in the string if it is to produce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonate as one full loop kdv4cy- e6y3y ($\frac{1}{2}\lambda$) when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in Fig. 12–36. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good?

  A person hears a pure tone in the 500–1000-Hz rano.uyl 9w7r2vege coming from two sources. The sound is loudest at points equidistant from the two sources. To determine exactly what the frequency is, the person moves about and finds that the sound level is minimal at a point 0.34 m farther from one source than the other. Wl7yu2vorw 9e.hat is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationary. The conductor on the -w+bskua u/t5teg p)1stationary train hears a 3.0-Hz beat frequency when the other train approaches. What is the speetua-p g+e uw/s1tbk) 5d of the moving train?   m/s

  The frequency of a steam train whistle as it apprbcedy/:b e5tiz .p8t-oaches you is 538 Hz. After it passes you, its frequency is m 8dt/tzcey5-e b: pib.easured as 486 Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimaib:x- oi 35pj;;f 2+yilw rpzuxpdg,,te the speed of cars just by listening to the difference in pitch of the engine noise between approaching and receding cars. Suppose the sound of a certain car drops by a full octave (frequency halved) as it goes by on the straightaway. How fau jpr;d lg,+25:z ixi;b oiw,y-xf3 ppst is it going?    m/s

  Two open organ pipes, sog3v cw3k; ( 9f/pnkizcunding together, produce a beat frequency of 11 Hz. The shorter one is 23i; /cv9gckfw pk(nz3.40 m long. How long is the other?    m

Two loudspeakers are at opposite e on3-cs .bwl8znds of a railroad car as it moves past a stationary observer at 10 m/s as shown in Fig. 12–37. If the speakers have identical sound frequencies of 212 Hz, what is the beat frequency heard by the observer when (a) he listens from the position bswz-o8lc 3.nA, in front of the car, (b) he is between the speakers, at B, and (c) he hears the speakers after they have passed him, at C?

  If the velocity of blood flow in the h8fwtam*5dkv (. v tw+aorta is normally about 0.32 m/s what beat frequentwt8v5kw .h+fvm (a*dcy would you expect if 5.50-MHz ultrasound waves were directed along the flow and reflected from the red blood cells? Assume that the waves travel with a speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.5 9qz;n onh8ey3,o -pgim/s while the moth is flying toward the bat at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is the frequency of the wave detected by the bat afteh3-nig9ypq,o 8oz n;e r that wave reflects off the moth?    kHz

  A bat emits a series of high frequency sound pulsesm 49c+nky 5ku. hiksf- as it approaches a moth. The pulses are approximately 70.0 ms apart, and kn 4cu-hkkmi.5y+fs9 each is about 3.0 ms long. How far away can the moth be detected by the bat so that the echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used tohgwt8;z howlw 4jua. +iwh-)9 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 3.4 m long, and it is called the F sharp (or G flat) horn. What is the fundamental frequency of this horn, and which overtone is close to F sharp? (See Table 12–3.) Model as an ou; )i89jwgw+.aw hhwt-h4loz pen tube.

  Room acoustics for stereo listening can be compromise,.-tj rp*vasw9i(xnqydx* 2 gd by the presence of standing waves, which can cause acoustic “dead spots” at the locations*yjt(xix- . 2wvpngr*q 9s a,d of the pressure nodes. Consider a living room 5.0 m long, 4.0 m wide, and 2.8 m high. Calculate the fundamental frequencies for the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involves a ld; r0i x(3pk7vq 3o lvece6g:xong, slender aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice, the rod can be made to “sing,” or emit a clear, lol 7rv x:g;6p3 diq0oeve(x3kc ud, ringing sound. For a 90-cm-long rod,
(a) what is the fundamental frequency of the sound?    $ \times10^{ 3}$ Hz
(b) What is its wavelength in the rod,    m
(c) what is the traveling wavelength in air at 20 $^{\circ} $ C?    m

  The intensity at the threshold of hearing for the human ear 7uo 5z bf16wiv7zhr 9eat a frequency of about 1009v5f1eziu7 wobz76 h r0 Hz is $I_0$ = $1 \times10^{12 } W / m^2$ for which $\beta$ the sound level, is 0 dB. The threshold of pain at the same frequency is about 120 dB, or $I$ = $1 W / m^2$ corresponding to an increase of intensity by a factor of $10^{12}$ By what factor does the displacement amplitude, A, vary? 10$^{a}$ a =   

  A plane is traveling at Mach 2.0. An observer on the gr) t 0zrphs4b3eu(r(xwejw m+ 1ound hears the sonic boom 1.5 min afterp 0(usw3tm1 ze+w exjrr4b)(h the plane passes directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is 15 8e*s,fiju b ,tkw*80lju i g:q$^{\circ} $ in a lake where the speed of the water wave is 2.2 km/h What is the speed of the boat?    km/h