Physics 41 Homework Set 3 Chapter 17 Serway 7 th Edition

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1 Pyic 41 Homework Set 3 Capter 17 Serway 7 t Edition Q: 1, 4, 5, 6, 9, 1, 14, 15 Quetion *Q17.1 Anwer. Te typically iger denity would by itelf make te peed of ound lower in a olid compared to a ga. Q17.4 Te peed of ound to two ignificant figure i. Let aume tat you can meaure time to 1 econd by uing a topwatc. To get a peed to two ignificant figure, you 10 need to meaure a time of at leat 1.0 econd. Since d= vt, te minimum ditance i 340 meter. *Q17.5 (i) Anwer. Te frequency increae by a factor of becaue te wave peed, wic i dependent only on te medium troug wic te wave travel, remain contant. (ii) Anwer (c). *Q17.9 Anwer (d). Te drop in intenity i wat we ould expect according to te invere-quare law: 4πr 1 P and 4πr P ould agree. (300 m) ( μw/m ) and (950 m) (0. μw/m ) are 0.18 W and 0.18 W, agreeing wit eac oter. Q17.1 Our brave Siberian aw te firt wave e encountered, ligt traveling 8 at m. At te ame moment, infrared a well a viible ligt began warming i kin, but ome time wa required to raie te temperature of te outer kin layer before e noticed it. Te meteor produced compreional wave in te air and in te ground. Te wave in te ground, wic can be called eiter ound or a eimic wave, traveled muc fater tan te wave in air, ince te ground i muc tiffer againt compreion. Our witne received it next and noticed it a a little eartquake. He wa no doubt unable to ditingui te P and S wave from eac oter. Te firt air-compreion wave e received wa a ock wave wit an amplitude on te order of meter. It tranported im off i doortep. Ten e could ear ome additional direct ound, reflected ound, and perap te ound of te falling tree. *Q17.14 In f'= (v + v o )f/(v v ) we can conider te ize of te fraction (v + v o )/(v v ) in eac cae. Te poitive direction i defined to run from te oberver toward te ource. In (a), 340/340 = 1 In, 340/(340 5) = 1.08 In (c), 340/( ) = 0.93 In (d), (340+5)/340 = 1.07 In (e), (340 5)/340 = 0.96 In (f) ( )/( ) = 1 In (g) (340 5)/(340 5) = 1. In order of decreaing ize we ave b > d > a = f = g > c > e. *Q17.15 (i) Anwer (c). Bot oberver and ource ave equal peed in oppoite direction relative to te medium, o in f'= (v + v o )f/(v v ) we would ave ometing like (340 5)f/(340 5) = f. (ii) Anwer (a). Te peed of te medium add to te peed of ound a far a te oberver i concerned, to caue an increae in λ = v/f. (iii) Anwer (a).

2 Problem: 3, 5, 7, 9, 11, 13, 17, 19, 3, 33, 38, 39,41 *P17.3 Te ound pule mut travel 150 m before reflection and 150 m after reflection. We ave d= vt d 300 m t = = = v 1533 m P17.5 Sound take ti time to reac te man: ( ) 0.0 m 1.75 m = m o te warning ould be outed no later tan = before te pot trike. 1 1 Since te wole time of fall i given by y = gt : 18.5 m = ( 9.80 m ) t t = 1.93 te warning need to come = 1.58 into te fall, wen te pot a fallen 1 ( 9.80 m )( 1.58 ) = 1. m to be above te ground by 0.0 m 1. m = 7.8 m 7. A cowboy tand on orizontal ground between two parallel vertical cliff. He i not midway between te cliff. He fire a ot, and ear it ecoe. Te econd eco arrive 1.9 after te firt, and 1.47 before te tird. Conider only te ound traveling parallel to te ground and reflecting from te cliff. Take te peed of ound a 340 m/. (a) Wat i te ditance between te cliff? Wat If? If e can ear a fourt eco, ow long after te tird eco doe it arrive? *P17.7 Let x1 repreent te cowboy ditance from te nearer canyon wall and x i ditance from te farter cliff. Te ound for te firt eco travel ditance x 1. For te econd, x. For te tird, x x1 x1+ x. For te fourt eco, x1 + x+ x1. Ten = 1.9 and x1+ x x 1 x = Tu m x = = and = ; x = 576 m. (a) So x1+ x = 86 m x + x + x x + x = 1.47

3 v 1500 m *P17.9 (a) If f =.4 M H z, λ = = = 6 f.4 10 v 1500 m If f = 1 M H z, λ = = = 6 f mm 1.50 mm m If f = 0 M H z, λ = = μm P17.11 (a) A =.00 μm π λ = = m = 40.0 cm 15.7 ω 858 v = = = 54.6 m k =.00co = μm 1 (c) v Aω ( μ ) max = =.00 m 858 = 1.7 mm 13. Write an expreion tat decribe te preure variation a a function of poition and time for a inuoidal ound wave in air, if λ = m and Δ Pmax = 0.00 N/m. π π P17.13 k= = = 6.8 m λ ( m ) ( m ) 1 π v π 343 m ω = = = λ Terefore, Δ = P 0.00 Pa in 6.8x m t. Write te function tat decribe te diplacement wave correponding to te preure wave in Problem 13. π v π 343 m 4 ω = π f= = = rad λ ( m ) ( 0.00 Pa) ΔP 8 = = =.5 10 m ρω v max max π π k = = = 6.8 m λ ( m ) ( 1.0 kg m )( 343 m )( ) 1 Terefore, maxco ( kx ω t) ( m ) co( 6.8x m t) = =.

4 P17.17 β 6 I = 10log = 10log 66.0 db 1 = I P17.19 I = ρω maxv (a) At f = 500 Hz, te frequency i increaed by a factor of.50, o te intenity (at contant ) increae by.50 = 6.5. max = 3.75 W m Terefore, W m 3. A family ice ow i eld at an encloed arena. Te kater perform to muic wit level 80.0 db. Ti i too loud for your baby, wo yell at 75.0 db. (a) Wat total ound intenity engulf you? Wat i te combined ound level? 1 P17.3 (a) ( β1 ) 1 = ( ) = ( ) I W m W m 10 or 4 I 1 = W m 1 ( β ) I = W m 10 = W m or I = W m = W m Wen bot ound are preent, te total intenity i I= I1+ I = W m W m = W m Te decibel level for te combined ound i W m 8 β = 10log 10log 1 ( = ) = W m 81. db..

5 P17.6 We preume te peaker broadcat equally in all direction. (a) r = + = AC P m 5.00 m W W m I = = = m π r π W m β = 10 dblog 1 10 W m β = 10 db 6.50 = 65.0 db r BC = 4.47 m W W m I = = m π β = 10 dblog 1 10 β = 67.8 db (c) I = 3.18 μw m μw m β = 10 dblog = 69.6 db 1 10 *P17.33 (a) f = ( + vo) ( v v ) f v ( ) ( ) f = 500 = 3.04 kh z (c) f = 500 =.08 khz 343 ( 40.0) f = 500 =.6 khz f = 500 =.40 khz 343 ( 40.0) wile police car overtake after police car pae

6 38. A iren mounted on te roof of a fireoue emit ound at a frequency of 900 Hz. A teady wind i blowing wit a peed of 15.0 m/. Taking te peed of ound in calm air to be 343 m/, find te wavelengt of te ound (a) upwind of te iren and downwind of te iren. Firefigter are approacing te iren from variou direction at 15.0 m/. Wat frequency doe a firefigter ear (c) if e or e i approacing from an upwind poition, o tat e i moving in te direction in wic te wind i blowing? (d) if e or e i approacing from a downwind poition and moving againt te wind? *P17.38 (a) Sound move upwind wit peed ( ) at frequency 900 Hz. Ten λ = v 38 m f = 900 = m. Cret pa a tationary upwind point m By imilar logic, ( + ) v m λ = = = f m (c) (d) Te ource i moving troug te air at 15 m/ toward te oberver. Te oberver i tationary relative to te air. v+ vo f = f = 900 Hz = 941 Hz v v Te ource i moving troug te air at 15 m/ away from te downwind firefigter. Her peed relative to te air i 30 m/ toward te ource. v+ vo f = f = 900 Hz = 900 Hz = 938 Hz v v P17.39 You ave to do firt! v 1 in θ = = ; θ = 19.5 v 3.00 S tanθ = ; x = x tan θ t = 0 θ x θ Oberver Oberver ear te boom a. b m m 56.6 km x = = = tan19.5 (a) It take te plane 4 x m t = = = 56.3 to travel ti ditance. v m S