Chaper 3 3 Vbraons and Waes PROBEM SOUIONS 3. (a) ang o he rgh as pose, he sprng orce acng on he bloc a he nsan o release s F s 30 N 0.3 7 N or 7 N o he le A hs nsan, he acceleraon s a F s 7 N 0.60 g 8 s or a 8 s o he le 3. When he objec coes o equlbru (a dsance 0 below he unsreched poson o he end o he sprng), F g and he orce consan s 0 0 g 0.5 g 9.80 s.6 0.59 03 N.59 N 3.3 (a) Snce he collson s perecl elasc, he ball wll rebound o he hegh o.00 beore cong o res oenarl. I wll hen repea hs oon oer and oer agan wh a regular perod. Fro a, wh 0 0, he e requred or he ball o reach he ground s 0.00 a 9.80 s 0.90 s hs s one-hal o he e or a coplee ccle o he oon. hus, he perod s.8 s. (c) No. he ne orce acng on he objec s a consan gen b F = g (ecep when s conac wh he ground). hs s no n he or o Hooe s law. 3. (a) he sprng consan s Page 3.
Chaper 3 Fs g 50 N 5.0 0 -.0 03 N F Fs.0 03 N 0.. 0 N he graph wll be a sragh lne passng hrough he orgn wh a slope equal o.0 03 N. 3.5 When he sse s n equlbru, he enson n he sprng F us equal he wegh o he objec. hus, g gng g 7.5 N 5.00 0 9.80 s 0. g 3.6 (a) he ree-bod dagra o he pon n he cener o he srng s gen a he rgh. Fro hs, we see ha F 0 F sn 35.0 0 or F 375 N sn 35.0 sn 35.0 37 N Snce he bow requres an appled horzonal orce o 375 N o hold he srng a 35.0 ro he ercal, he enson n he sprng us be 375 N when he sprng s sreched 30.0 c. hus, he sprng consan s F 375 N 0.300.5 03 N 3.7 (a) When he bloc coes o equlbru, F 0 g 0 gng 0 g 0.0 g 9.80 s 75 N 0.06 or he equlbru poson s 0.06 below he unsreched poson o he lower end o he sprng. When he eleaor (and eerhng n ) has an upward acceleraon o a.00 s second law o he bloc ges, applng Newon s F 0 g a or 0 F g a Page 3.
Chaper 3 where = 0 a he equlbru poson o he bloc. Snce 0 g 0 [see par (a)], hs becoes a and he new poson o he bloc s a 0.0 g.00 s 75 N. 0. c or. c below he equlbru poson. (c) When he cable breas, he eleaor and s conens wll be n ree-all wh a = g. he new equlbru poson o he bloc s ound ro F 0 g g, whch elds 0 0 snapped, he bloc was a res relae o he eleaor a dsance. When he cable 0 0.06 0.0 0.8 below he new equlbru poson. hus, whle he eleaor s n ree-all, he bloc wll oscllae wh aplude 0.8 abou he new equlbru poson, whch s he unsreched poson o he sprng s lower end. 3.8 (a) When he gun s red, he elasc poenal energ nall sored n he sprng s ransored no nec energ o he projecle. hus, s necessar o hae 0 0 or 0 0 3.00 0 3 g 5.0 s 8.00 0 99 N he agnude o he orce requred o copress he sprng 8.00 c and load he gun s Fs 99 N 8.00 0 75.9 N 3.9 (a) Assue he rubber bands obe Hooe s law. hen, he orce consan o each band s F s 5 N.0 0 -.5 03 N hus, when boh bands are sreched 0.0, he oal elasc poenal energ s PEs 3.5 0 N 0.0 60 J Conseraon o echancal energ ges KE PE s KE PE s, or Page 3.3
Chaper 3 0 0 60 J, so 60 J 50 0-3 g 9 s 3.0 (a) F a a 30 N 0.00 575 N wor done PEs 575 N 0.00 6.0 J 3. Fro conseraon o echancal energ, KE PE g PE s KE PE g PE s or 0 gh 0 0 0 gng gh 0.00 g 9.80 s 0.600.00 0.9 03 N 3. Conseraon o echancal energ, ( KE PEg PEs ) ( KE PEg PE s), ges 0 0 0 0, or 5.00 06 N 3.6 0.3 s 000 g 3.3 An unnown quan o echancal energ s conered no nernal energ durng he collson. hus, we appl conseraon o oenu ro jus beore o jus aer he collson and oban + M(0) = (M + )V, or he speed o he bloc and ebedded bulle jus aer collson s V M 0.0 0 3 g.0 g 300 s.9 s Now, we use conseraon o echancal energ ro jus aer collson unl he bloc coes o res. hs ges 0 M V, or V M.0 g.9 s 0.77 9.6 N Page 3.
Chaper 3 3. (a) A eher o he urnng pons, = A, he consan oal energ o he sse s oenarl sored as elasc poenal energ n he sprng. hus, E A. When he objec s dsance ro he equlbru poson, he elasc poenal energ s PEs and he nec energ s KE. A he poson where KE = PE s, s necessar ha or (c) When KE = PE, conseraon o energ ges E KE PEs PEs PEs 3PE s, or A 3 A 3 or A 3 3.5 (a) A au dsplaceen ro equlbru, all o he energ s n he or o elasc poenal energ, gng E, and a E a 7.0 J 0.0.63 03 N A he equlbru poson ( = 0), he sprng s oenarl n s relaed sae and PE s = 0, so all o he energ s n he or o nec energ. hs ges KE 0 a E 7.0 J (c) I, a he equlbru poson, = a = 3.5 /s, he ass o he bloc s E a 7.0 J 3.5 s 7.90 g (d) A an poson, he consan oal energ s, E KE PE, so a = 0.60 s E 7.0 J.63 03 N 0.60 7.90 g.57 s (e) A = 0.60, where =.57 /s, he nec energ s Page 3.5
Chaper 3 7.90 g.57 s 6. J KE () A = 0.60, where KE = 6. J, he elasc poenal energ s PEs E KE 7.0 J 6. J 0.9 J or alernael, 3.63 0 N 0.60 0.9 J PEs (g) A he rs urnng pon (or whch < 0 snce he bloc sared ro res a = +0.0 and has passed hrough he equlbru a = 0) all o he reanng energ s n he or o elasc poenal energ, so E E loss 7.0 J.0 J 33.0 J and 33.0 J 33.0 J.63 03 N 0.0 3.6 (a) F 83.8 N 5.6 0.58 N E PEs 83.8 N 5.6 0 0.5 J (c) Whle he bloc was held saonar a = 5.6 c, F F F 0, or he sprng orce was equal n agnude and opposel dreced o he appled orce. When he appled orce s suddenl reoed, here s a ne orce F s =.58 N dreced oward he equlbru poson acng on he bloc. hs ges he bloc an acceleraon hang agnude s a F s.58 N 0.50 g 8.3 s (d) A he equlbru poson, PE s = 0, so he bloc has nec energ KE = E = 0.5 J and speed E 0.5 J 0.50 g.00 s Page 3.6
Chaper 3 (e) I he surace was rough, he bloc would spend energ oercong a reardng rcon orce as oed oward he equlbru poson, causng o arre a ha poson wh a lower speed han ha copued aboe. Copung a nuber alue or hs lower speed requres nowledge o he coecen o rcon beween he bloc and surace. 3.7 Fro conseraon o echancal energ, KE PE PE KE PE PE g s g s we hae 0 0 0 A, or A (a) he speed s a au a he equlbru poson, = 0. a A 9.6 N 0.00 0.8 s 0.0 g When = 0.05, 9.6 N 0.00 0.05 0.6 s 0.0 g (c) When = +0.05, 9.6 N 0.00 0.05 0.6 s 0.0 g (d) I a, hen A A hs ges A = A /, or A 3 /.0 c 3 / 3.5 c. 3.8 (a) KE = 0 a = A, so E KE PE 0 A, or he oal energ s s E 50 N 0.035 A 0.5 J Page 3.7
Chaper 3 he au speed occurs a he equlbru poson where PE s = 0. hus, E a, or a E 50 N A 0.035 0.78 s 0.50 g (c) he acceleraon s a F/ /. hus, a = a a a = a = A. a a A A 50 N 0.035 8 s 0.50 g 3.9 he au speed occurs a he equlbru poson and s a A hus, A a 6.0 N 0.00 0.00 s.00 g, and Fg g.00 g 9.80 s 39. N 3.0 A 0.0 N 50.0 0-3 g 0.50 0.5 3.06 s 3. (a) he oon s sple haronc because he re s roang wh consan eloc and ou are loong a he unor crcular oon o he bup projeced on a plane perpendcular o he re. Noe ha he angenal speed o a pon on he r o a rollng re s he sae as he ranslaonal speed o he ale. hus, 3.00 s and he angular eloc o he re s car r 3.00 s 0.300 0.0 rad s hereore, he perod o he oon s 0.0 rad s 0.68 s Page 3.8
Chaper 3 3. (a) r 0.00.00 s 0.68 s.00 s 0.500 Hz (c).00 s 3. rad s 3.3 he angle o he cran pn s. Is -coordnae s Acos Acos where A s he dsance ro he cener o he wheel o he cran pn. hs s o he correc or o descrbe sple haronc oon. Hence, one us conclude ha he oon s ndeed sple haronc. 3. he perod o braon or an objec-sprng sse s. hus, = 0.3 s and = 35. g = 35. 0 3 g, he orce consan o he sprng s 35. 0 3 g 0.3 s 8. N 3.5 he sprng consan s ound ro Fs g 0.00 g 9.80 s 3.9 0 -.5 N When he objec aached o he sprng has ass = 5 g, he perod o oscllaon s 0.05 g 0.63 s.5 N 3.6 he sprngs copress 0.80 c when supporng an addonal load o = 30 g. hus, he sprng consan s g 30 g 9.80 s 0.80 0-3.9 05 N When he ep car, M =.0 0 3 g, oscllaes on he sprngs, he requenc wll be Page 3.9
Chaper 3 3.9 05 N M.0 03 g. Hz 3.7 (a) he perod o oscllaon s where s he sprng consan and s he ass o he objec aached o he end o he sprng. Hence, 0.50 g.0 s 9.5 N I he car s released ro res when s.5 c ro he equlbru poson, he aplude o oscllaon wll be A =.5 c =.5 0. he au speed s hen gen b a A A 9.5 N 0.50 g.5 0 0.8 s (c) When he car s c ro he le end o he rac, has a dsplaceen o = c c =.0 c ro he equlbru poson. he speed o he car a hs dsance ro equlbru s 9.5 N A 0.05 0.00 0.5 s 0.50 g 3.8 he general epresson or he poson as a uncon o e or an objec undergong sple haronc oon wh = 0 a = 0 s Asn. hus, 5. c sn 8.0, we hae ha he aplude s A = 5. c and he angular requenc s 8.0 rad s. (a) he perod s 8.0 s - 0.5 s he requenc o oon s 0.5 s.0 s-.0 Hz (c) As dscussed aboe, he aplude o he oon s A 5. c (d) Noe: For hs par, our calculaor should be se o operae n radans ode. Page 3.0
Chaper 3 I =.6 c, hen A.6 c 5. c sn sn sn 0.50 0.5 radans and 0.5 rad 0.5 rad 8.0 rad s. 0 s 0 3 s s 3.9 (a) A he equlbru poson, he oal energ o he sse s n he or o nec energ and a E, so he au speed s a E 5.83 J 0.36 g 5.98 s he perod o an objec-sprng sse s, so he orce consan o he sprng s 0.36 g 0.50 s 06 N (c) A he urnng pons, = A, he oal energ o he sse s n he or o elasc poenal energ, or E A, gng he aplude as A E 5.83 J 06 N 0.38 3.30 For a sse eecung sple haronc oon, he oal energ a be wren as s a E KE PE A, where A s he aplude and a s he speed a he equlbru poson. Obsere ro hs epresson, ha we a wre a A. (a) I, hen a E a becoes a a and ges Page 3.
Chaper 3 3 3 3A a A or A 3 I he elasc poenal energ s PE s = E/, we hae A or A and A 3.3 (a) A = 3.50 s, F N rad 5.00 (3.00 ) cos.58 (3.50 s).0 N s, or F.0 N dreced o he le he angular requenc s 5.00 N.00 g.58 rad s and he perod o oscllaon s 3.97 s..58 rad s Hence he nuber o oscllaons ade n 3.50 s s N 3.50 s 3.97 s 0.88 3.3 (a) F 7.50 N 3.00 0-50 N 50 N 0.500 g. rad s Page 3.
Chaper 3. rad s 3.56 Hz 3.56 Hz 0.8 s (c) A = 0, = 0 and = 5.00 0, so he oal energ o he oscllaor s E KE PEs 0 50 N 5.00 0 0.33 J (d) When = A, 0 so E KE PE 0 s A. hus, A E 0.33 J 50 N/ 5.00 0 5.00 c (e) A = 0, KE a E, or a E 0.33 J 0.500 g. s a a F a A 50 N 5.00 0 0.500 g 5.0 s Noe: o sole pars () and (g), our calculaor should be se n radans ode. () A = 0.500 s, Equaon 3.a ges he dsplaceen as 50 N A cos A cos 5.00 c cos 0.500 s 0.99 c 0.500 g (g) Fro Equaon 3.b, he eloc a = 0.500 s s A sn A sn 50 N 50 N 0.500 g 0.500 g 5.00 0 - sn 0.500 s.0 Page 3.3
Chaper 3 and ro Equaon 3.c, he acceleraon a hs e s a A cos A cos 50 N 50 N 5.00 0 cos 0.500 s.59 s 0.500 g 0.500 g - 3.33 Fro Equaon 3.6, A A Hence, A A cos A cos A sn Fro Equaon 3., a A cos A cos 3.3 (a) he hegh o he ower s alos he sae as he lengh o he pendulu. Fro g, we oban 9.80 s 5.5 s g 59.6 On he Moon, where g =.67 /s, he perod wll be 59.6 37.5 s g.67 s 3.35 he perod o a pendulu s he e or one coplee oscllaon and s gen b g, where l s he lengh o he pendulu. (a) 3.00 n 60 s 0 oscllaons n.50 s he lengh o he pendulu s g.50 s 9.80 s 0.559 Page 3.
Chaper 3 3.36 he perod n oo s / g and he perod n Cabrdge s C C / g C. We now ha = C =.000 s, ro whch, we see ha g C g g, or C C 0.99 C g 0.99 7.00 5 3.37 (a) he perod o he pendulu s g. hus, on he Moon where he ree-all acceleraon s saller, he perod wll be longer and he cloc wll run slow. he rao o he pendulu s perod on he Moon o ha on Earh s Moon Earh gmoon gearh 9.80 g g.63 Earh Moon.5 Hence, he pendulu o he cloc on Earh aes.5 cs whle he cloc on he Moon s ang.00 c. Aer he Earh cloc has ced o.0 h and agan reads :00 dngh, he Moon cloc wll hae ced o.0 h/.5 = 9.80 h and wll read 9 : 8 AM. 3.38 (a) he lower eperaure wll cause he pendulu o conrac. he shorer lengh wll produce a saller perod, so he cloc wll run aser or gan e. he perod o he pendulu s 0 / g a 0 C, and a 5.0 C s / g. he rao o hese perods s 0 / 0 /. Fro Chaper 0, he lengh a 5.0 C s 0 Al0, so 0 6 Al( ) 0.999 0 C 5.0 C 0 C.000 6 hs ges 0 0.000 6.000 3 hus n one hour (3 600 s), he chlled pendulu wll gan.000 3 3 600 s. s. 3.39 (a) Fro g, he lengh o a pendulu wh perod s = g /. Page 3.5
Chaper 3 On Earh, wh =.0 s, 9.80 s.0 s 0.5 5 c I =.0 s on Mars, 3.7 s.0 s 0.09 9. c he perod o an objec on a sprng s, whch s ndependen o he local ree-all acceleraon. hus, he sae ass wll wor on Earh and on Mars. hs ass s 0 N.0 s 0.5 g 3.0 he apparen ree-all acceleraon s he ecor su o he acual ree-all acceleraon and he negae o he eleaor s acceleraon. o see hs, consder an objec ha s hangng ro a ercal srng n he eleaor and appears o be a res o he eleaor passengers. hese passengers belee he enson n he srng s he negae o he objec s wegh, or g app where app g s he apparen ree-all acceleraon n he eleaor. An obserer locaed ousde he eleaor apples Newon s second law o hs objec b wrng F g a e where e ae g g app, whch ges app e a s he acceleraon o he eleaor and all s conens. hus, g g a. (a) I we choose downward as he pose drecon, hen a 5.00 s n hs case and g 9.80 5.00 s.8 s app (downward). he perod o he pendulu s e 5.00 3.65 s g.8 s app Agan choosng downward as pose, a 5.00 s and g 9.80 5.00 s.80 s (downward) n hs case. he perod s now gen b e app 5.00 6. s g.80 s app Page 3.6
Chaper 3 (c) I a 5.00 s horzonall, he ecor su gapp g a e s e as shown n he sech a he rgh. he agnude s g app 5.00 s 9.80 s.0 s and he perod o he pendulu s 5.00. s g.0 s app 3. (a) he dsance ro he boo o a rough o he op o a cres s wce he aplude o he wae. hus, A = 8.6 c and A.3 c he horzonal dsance ro a cres o a rough s a hal waelengh. Hence, 5.0 c and 0. c Fgure P3. (c) he perod s 8.0 s 5.56 0 s (d) he wae speed s 0. c 8.0 s 87 c s.87 s 3. (a) he aplude s he agnude o he au dsplaceen ro equlbru (a = 0). hus, A.00 c he perod s he e or one ull ccle o he oon. hereore,.00 s (c) he perod a be wren as requenc s, so he angular Fgure P3..00 s rad s Page 3.7
Chaper 3 (d) he oal energ a be epressed as E A. hus, a A /, and snce, hs becoes a A and elds a a A rad s.00 c c s (e) he sprng eers au orce, F, when he objec s a au dsance ro equlbru,.e., a A.00 c. hus, he au acceleraon o he objec s a A F aa A rad s.00 c.93 c s () he general equaon or poson as a uncon o e or an objec undergong sple haronc oon wh = 0 when = 0 s = A sn ( ). For hs oscllaor, hs becoes.00 c sn 3.3 (a) he perod and he requenc are recprocals o each oher. hereore, 0.9 MHz 0.9 0 s 6 9.8 0 9 s 9.8 ns 3.00 08 s 0.9 0 s 6.9 3. (a) he requenc o a ranserse wae s he nuber o cress ha pass a gen pon each second. hus, 5.00 cress pass n.0 seconds, he requenc s 5.00.0 s 0.357 s 0.357 Hz he waelengh o he wae s he dsance beween successe aa or successe na. hus,.76 and he wae speed s.76 0.357 s 0.985 s 3.5 he speed o he wae s Page 3.8
Chaper 3 5 c.5 c s 0.0 s and he requenc s 0.0 b 30.0 s.33 Hz hus,.5 c s.33 Hz 3.9 c 3.6 Fro =, he waelengh (and sze o salles deecable nsec) s 30 s 60.0 03 Hz 5.67 0-3 5.67 3.7 he requenc o he wae (ha s, he nuber o cress passng he cor each second) s.00 s- and he waelengh (dsance beween successe cress) s 8.50 c. hus, he wae speed s 8.50 c.00 s- 7.0 c s 0.70 s and he e requred or he rpples o rael 0.0 oer he surace o he waer s 0.0 0.70 s 58.8 s 3.8 (a) When he boa s a res n he waer, he speed o he wae relae o he boa s he sae as he speed o he wae relae o he waer,.0 s. he requenc deeced n hs case s.0 s 0 0.0 Hz ang easward as pose, wae, boa wae, waer boa, waer (see he dscusson o relae eloc n Chaper 3 o he eboo) ges wae, boa.0 s.0 s 5.0 s and boa, wae wae, boa 5.0 s hus, Page 3.9
Chaper 3 boa wae, 5.0 s 0 0.5 Hz 3.9 he down and bac dsance s.00 +.00 = 8.00. he speed s hen d oal 8.00 0.800 s 0.0 s F Now, 0.00 g.00 5.00 0 g so F 5.00 0 g 0.0 s 80.0 N 3.50 he speed o he wae s 0.0 0.800 s 5.0 s and he ass per un lengh o he rope s / 0.350 g. hus, ro F, we oban 5.0 s 0.350 g 9 N F 3.5 (a) he speed o ranserse waes n he cord s F, where s he ass per un lengh. Wh he enson n he cord beng F =.0 N, he wae speed s F F F.0 N 6.30 0.50 g. s he e o rael he lengh o he cord s 6.30. s 0.8 s 3.5 (a) In ang 6 round rps, he pulse raels he lengh o he lne es or a oal dsance o. he speed o he pulse s hen Page 3.0
Chaper 3.0.96 s 8.6 s he speed o ranserse waes n he lne s F, so he enson n he lne s 0.375 g F.0 8.6 s 73.8 N 3.53 (a) he ass per un lengh s 0.0600 g 5.00 0.00 g Fro F, he requred enson n he srng s F 50.0 s 0.00 g 30.0 N, F 8.00 N 0.00 g 5.8 s 3.5 he ass per un lengh o he wre s.00 0-3 g.60.50 0-3 g and he speed o he pulse s.60 0.036 s.3 s hus, he enson n he wre s F -3.3 s.50 0 g.9 N Bu, he enson n he wre s he wegh o a 3.00-g objec on he Moon. Hence, he local ree-all acceleraon s g F.9 N 3.00 g.6 s 3.55 he perod o he pendulu s / g, so he lengh o he srng s Page 3.
Chaper 3 9.80 s.00 s g 0.993 hen ass per un lengh o he srng s hen 0.060 0 g g 0.060 0.993 When he pendulu s ercal and saonar, he enson n he srng s F Mball g 5.00 g 9.80 s 9.0 N and he speed o ranserse waes n s F 9.0 N 0.060 g 8.5 s 3.56 I s he ass per un lengh or he rs srng, hen s ha o he second srng. hus, wh F F F, he speed o waes n he second srng s F F F 5.00 s 7.07 s 3.57 (a) he enson n he srng s F g 3.0 g 9.80 s 9 N. hen, ro F, he ass per un lengh s F 9 N s 0.05 g When =.00 g, he enson s F g.0 g 9.80 s 0 N and he speed o ranserse waes n he srng s F 0 N 0.05 g 0 s 3.58 I he enson n he wre s F, he ensle sress s Sress = F/A, so he speed o ranserse waes n he wre a be wren as Page 3.
Chaper 3 F A Sress Sress / /( A ) Bu, Sress A V =olue, so A dens. hus,. When he sress s a s au, he speed o waes n he wre s ( Sress) 9 a.70 0 Pa a 3 3 7.86 0 g/ 586 s 3.59 (a) he speed o ranserse waes n he lne s F, wh beng he ass per un lengh. hereore, F F F.5 N 38.0.65 g 3. s he worer could hrow an objec, such as a snowball, a one end o he lne o se up a pulse, and use a sopwach o easure he e aes a pulse o rael he lengh o he lne. Fro hs easureen, he wo rer would hae an esae o he wae speed, whch n urn can be used o esae he enson. 3.60 (a) In ang n round rps along he lengh o he lne, he oal dsance raeled b he pulse s n n. he wae speed s hen n Fro F as he speed o ranserse waes n he lne, he enson s F M n M n n M 3.6 (a) Consruce nererence produces he au aplude Aa A A 0.50 Desruce nererence produces he nu aplude Page 3.3
Chaper 3 An A A 0.0 3.6 We are gen ha Acos( ) (0.5 )cos(0. ). (a) B nspecon, he aplude s seen o be A 0.5 he angular requenc s 0. rad s. Bu, so he sprng consan s (0.30 g)(0. rad s) 0.7 N (c) Noe: Your calculaor us be n radans ode or par (c). A = 0.30 s, 0.5 cos 0. rad s 0.30 s 0.3 (d) Fro conseraon o echancal energ, he speed a dsplaceen s gen b A. hus, a = 0.30 s, when = 0.3, he speed s 0. rad s (0.5 ) (0.3 ) 0. s 3.63 (a) he perod o a brang objec-sprng sse s, so he sprng consan s.00 g 0.600 s 9 N I =.05 s or ass, hs ass s (9 N/)(.05 s) 6. g 3.6 (a) he perod s he recprocal o he requenc, or 96 s 5.0 0 3 s 5.0 s sound 33 s 96 s.75 3.65 (a) he perod o a sple pendulu s g, so he perod o he rs sse s Page 3.
Chaper 3 0.700.68 s g 9.80 s he perod o ass-sprng sse s, so he perod o he second sse s =, hen l g and he sprng consan s g.0 g 9.80 s 0.700 6.8 N 3.66 Snce he sprng s lgh, we neglec an sall aoun o energ los n he collson wh he sprng, and appl conseraon o echancal energ ro when he bloc rs sars unl coes o res agan. hs ges KE PE g PE s KE PE g PE s, or 0 0 0 0 a gh hus, a gh 0.500 g 9.80 s.00 0.0 N 0.990 3.67 Choosng PE g = 0 a he nal hegh o he bloc, conseraon o echancal energ ges KE PE PE KE PE PE, or g s g s g 0, where s he speed o he bloc aer allng dsance. (a) When = 0, he non-zero soluon o he energ equaon ro aboe ges 3.00 g 9.80 s a a g or g a 0.00 588 N When = 5.00 c = 0.050 0, he energ equaon ges g, or Page 3.5
Chaper 3 588 N 0.050 0 9.80 s 0.050 0 0.700 s 3.00 g 3.68 (a) We appl conseraon o echancal energ ro jus aer he collson unl he bloc coes o res. KE PE s KE PE s ges 0 0 MV or he speed o he bloc jus aer he collson s V M 900 N 0.050 0.00 g.50 s Now, we appl conseraon o oenu ro jus beore pac o edael aer he collson. hs ges 0 MV bulle bulle or M bulle bulle V.00 g 00 s.5 s 00 s 5.00 0-3 g he echancal energ conered no nernal energ durng he collson s bulle bulle E KE KE MV or E 3 5.00 0 g 00 s 00 s.00 g.50 s E 37 J 3.69 Choose PE g = 0 when he blocs sar ro res. hen, usng conseraon o echancal energ ro when he blocs are released unl he sprng reurns o s unsreched lengh ges KE PE PE KE PE PE, or g s g s Page 3.6
Chaper 3 g sn 0 g 0 0 0 5 30 g 5 g 9.80 s 0.00 sn 0 30 g 9.80 s 0.00 00 N 0.00 eldng. s 3.70 (a) When he gun s red, he energ nall sored as elasc poenal energ n he sprng s ransored no nec energ o he bulle. Assung no loss o energ, we hae, or 9.80 N 0.00 9.8 s.00 0 3 g Fro a, he e requred or he pelle o drop.00 o he loor, sarng wh 0 0, s 0.00 a 9.80 s 0.5 s he range (horzonal dsance raeled durng he lgh) s hen 0 9.8 s 0.5 s 8.9 Page 3.7
Chaper 3 3.7 he ree-bod dagra a he rgh shows he orces acng on he balloon when s dsplaced dsance s = along he crcular arc ollows. he ne orce angenal o hs pah s F F Bsn g sn B g sn ne For sall angles, sn s/ Also, g He V g and he buoan orce s acng on he balloon s B ar V g. hus, he ne resorng orce F ne ar He Vg s Obsere ha hs s n he or o Hooe s law, F s, wh ar He Vg hus, he oon wll be sple haronc and he perod s gen b HeV He Vg g ar He ar He hs elds 0.80 3.00.0 s.9 0.80 9.80 s 3.7 (a) When he bloc s gen soe sall upward dsplaceen, he ne resorng orce eered on b he rubber bands s F F F sn, where an ne For sall dsplaceens, he angle wll be er sall. hen sn an s, and he ne resorng orce Page 3.8
Chaper 3 F Fne F he ne resorng orce ound n par (a) s n he or o Hooe s law F =, wh = F/. hus, he oon wll be sple haronc, and he angular requenc s F 3.73 Newon s law o graaon s GM F, where M r r 3 3 hus, F= 3 G r whch s o Hooe s law or, F r, wh = 3 G 3.7 he nner p o he wng s aached o he end o he sprng and alwas oes wh he sae speed as he end o he brang sprng. hus, s au speed s.7 0 N nner, a sprng, a 3 A 0.0 c 0.5 c s 0.30 0 g reang he wng as a rgd bar, all pons n he wng hae he sae angular eloc a an nsan n e. As he wng rocs on he ulcru, he nner p and ouer ps ollow crcular pahs o deren rad. Snce he angular eloces o he ps are alwas equal, we a wre r ouer ouer r nner nner he au speed o he ouer p s hen Page 3.9
Chaper 3 r ouer ouer, a nner, a rnner 5.0 0.5 c s.3 c s 3.00 3.75 (a) 500 N.00 g 5.8 rad s Appl Newon s second law o he bloc whle he eleaor s accelerang: F Fs g a Wh F and a g 3, hs ges g g 3, or s g.00 g 9.80 s 3 3 500 N 5.3 0 5.3 c 3.76 (a) Noe ha as he sprng passes hrough he ercal poson, he objec s ong n a crcular arc o radus. Also, obsere ha he -coordnae o he objec a hs pon us be negae 0 so he sprng s sreched and eerng an upward enson orce o agnude greaer han he objec s wegh. hs s necessar so he objec eperences a ne orce oward he po o suppl he needed cenrpeal acceleraon n hs poson. hs s suarzed b Newon s second law appled o he objec a hs pon, sang F g Conseraon o energ requres ha E KE PEg, PEs, KE PEg, PE s,, or E 0 g 0 g, reducng o g (c) Fro he resul o par (a), obsere ha ( )( g ). Subsung hs no he resul ro par ges g( ) ( )( g). Aer epandng and regroupng ers, hs becoes ( ) (3 g ) ( 3 g ) 0, whch s a quadrac equaon a b c 0, wh a 50 N.50 03 N b 3g 3 5.00 g 9.80 s 50 N.50.73 03 N and Page 3.30
Chaper 3 c 3g 3 5.00 g 9.80 s.50 N Applng he quadrac orula, eepng onl he negae soluon [see he dscusson n par (a)] ges b b ac 3 3 3.73 0.73 0.50 0 a.50 0 3 or 0.0 (d) Because he lengh o hs pendulu ares and s longer hroughou s oon han a sple pendulu o lengh, s perod wll be longer han ha o a sple pendulu. 3.77 he au acceleraon o he oscllang sse s a A A a he rcon orce eered beween he wo blocs us be capable o accelerang bloc B a hs rae. When bloc B s on he erge o slppng, n g a and we us hae s s a s s a aa A sg hus, A s g 0.600 9.80 s.50 Hz 6.6 0 6.6 c Page 3.3