1、4.MechanicsMultipleChoice20041.Thegraphaboveshowsvelocityvversustimetforanobjectinlinearmotion.Whichofthefollowingisapossiblegraphofpositionxversustimetforthisobject?2.Anobjectisdroppedfromrestfromthetopofa400mcliffonEarth.Ifairresistanceisnegligible,whatisthedistancetheobjecttravelsduringthefirst6s

2、ofitsfall?30m(B)60m(C)120m(D)180m(E)360m3.A2kgballcollideswiththeflooratanangle0andreboundsatthesameangleandspeedasshownabove.Whichofthefollowingvectorsrepresentstheimpulseexertedontheballbythefloor?(A)(B)Threeblocksofmasses3m,2m,andmareconnectedtostringsA,B,andCasshownabove.Theblocksarepulledalonga

3、roughsurfacebyaforceofmagnitudeFexertedbystringC.Thecoefficientoffrictionbetweeneachblockandthesurfaceisthesame.Whichstringmustbethestrongestinordernottobreak?(A)A(B)B(C)C(D)Theymustallbethesamestrength.(E)Itisimpossibletodeterminewithoutknowingthecoefficientoffriction.Questions5-6Ablockofmass3kg,in

4、itiallyatrest,ispulledalongafrictionless,horizontalsurfacewithaforceshownasafunctionoftimetbythegraphabove.5.Theaccelerationoftheblockatt=2sis(A)3/4m/s2(B)4/3m/s2(C)2m/s2(D)8m/s2(E)12m/s26.Thespeedoftheblockatt=2sis(A)4/3m/s(B)8/3m/s(C)4m/s(D)8m/s(E)24m/sQuestions7-87.AsphereofmassM,radiusr,androtat

5、ionalinertiaIisreleasedfromrestatthetopofaninclinedplaneofheighthasshownabove.Iftheplaneisfrictionless,whatisthespeedvcm,ofthecenterofmassofthesphereatthebottomoftheincline?(A)麗(B)普(C)2Mghr2(E):2Mghr2I+Mr28.Iftheplanehasfrictionsothatthesphererollswithoutslipping,whatisthespeedvcmofthecenterofmassat

6、thebottomoftheincline?(A)m,areconnectedbyalightstring.Thestringpassesoverafrictionlesspulleyofnegligiblemasssothattheblockshangvertically.Theblocksarethenreleasedfromrest.WhatistheaccelerationoftheblockofmassM?(A)g(D)(E)Foraparticularnonlinearspring,therelationshipbetweenthemagnitudeoftheappliedforc

7、eFandtheresultantdisplacementxfromequilibriumisgivenbytheequationF=kx2.Whatistheamountofworkdonebystretchingthespringadistancexo?(A)kx3(B)1/2kx(C)1/2kx3(D)1/3kx2(E)1/3kx3oooooQuestions22-23BoatmovesforwardBoatmovesbackwardBoatdoesnotmoveBoatdoesnotmoveBoatmovesforwardTwopucksmovingonafrictionlessair

8、tableareabouttocollide,asshownabove.The1.5kgpuckismovingdirectlyeastat2.0m/s.The4.0kgpuckismovingdirectlynorthat1.0m/s.Whatisthetotalkineticenergyofthetwo-pucksystembeforethecollision?(A)tT3J(B)5.0J(C)7.0J(D)10J(E)11JWhatisthemagnitudeofthetotalmomentumofthetwo-pucksystemafterthecollision?(A)1.0kgm/

9、s(B)3.5kgm/s(C)5.0kgm/s(D)7.0kgm/s(E)5.5：5kgm/sThepositionofanobjectisgivenbytheequationx=3.0t2+1.5t+4.5,wherexisinmetersandtisinseconds.Whatistheinstantaneousaccelerationoftheobjectatt=3.0s?(A)3.0m/s2(B)6.0m/s2(C)9.0m/s2(D)19.5m/s2(E)36m/s2Asshownabove,twostudentssitatoppositeendsofaboatthatisiniti

10、allyatrest.Thestudentinthefrontthrowsaheavyballtothestudentintheback.Whatisthemotionoftheboatatthetimeimmediatelyaftertheballisthrownand,later,aftertheballiscaught?(Assumethatairandwaterfrictionarenegligible.)ImmediatelyAftertheThrowAftertheCatchBoatmovesforwardBoatmovesforwardBoatmovesforwardBoatmo

11、vesbackwardBoatmovesbackward(B)(T1+T2)R=Ia(C)T2R=Ia(D)(T2-T/R=Ia(E)(m2-m)gR=laTwoblocksarejoinedbyalightstringthatpassesoverthepulleyshownabove,whichhasradiusRandmomentofinertiaIaboutitscenter.T1andT2arethetensionsinthestringoneithersideofthepulleyandaistheangularaccelerationofthepulley.Whichofthefo

12、llowingequationsbestdescribesthepulleysrotationalmotionduringthetimetheblocksaccelerate?(A)m2gR=IaThegraphaboveshowstheforceofgravityonasmallmassasafunctionofitsdistanceRfromthecenteroftheEarthofradiusRe,iftheEarthisassumedtohaveauniformdensity.Theworkdonebytheforceofgravitywhenthesmallmassapproache

13、sEarthfromfarawayandisplacedintoacircularorbitofradiusR2isbestrepresentedbytheareaunderthecurvebetween(A)R=0andR=Re,(B)R=0andR=R2(C)R=Re,andR=R2(D)R=ReandR=卷(E)R=R?andRAhorizontalforceFpushesablockofmassmagainstaverticalwall.Thecoefficientoffrictionbetweentheblockandthewallisy.WhatvalueofFisnecessar

14、ytokeeptheblockfromslippingdownthewall?(A)mg(B)ymg(C)mg/y(D)mg(1-y)(E)mg(1+y)AmassMsuspendedbyaspringwithforceconstantkhasaperiodTwhensetintooscillationonEarth.ItsperiodonMars,whosemassisabout1/9andradius1/2thatofEarth,ismostnearly(A)1/3T(B)2/3T(C)T(D)3/2T(E)3TA1000Welectricmotorliftsa100kgsafeatcon

15、stantvelocity.Theverticaldistancethroughwhichthemotorcanraisethesafein10sismostnearly(A)1m(B)3m(C)I0m(D)32m(E)100mA1.0kgmassisattachedtotheendofaverticalidealspringwithaforceconstantof400N/m.Themassissetinsimpleharmonicmotionwithanamplitudeof10cm.Thespeedofthe1.0kgmassattheequilibriumpositionis(A)2m

16、/s(B)4m/s(C)20m/s(D)40m/s(E)200m/sAstudentistestingthekinematicequationsforuniformlyacceleratedmotionbymeasuringthetimeittakesforlight-weightplasticballstofalltothefloorfromaheightof3minthelab.Thestudentpredictsthetimetofallusinggas9.80m/s2butfindsthemeasuredtimetobe35%greater.Whichofthefollowingist

17、hemostlikelycauseofthelargepercenterror?Theaccelerationduetogravityis70%greaterthan9.80m/s2atthislocation.Theaccelerationduetogravityis70%lessthan9.80m/s2atthislocation.Airresistanceincreasesthedownwardacceleration.Theaccelerationoftheplasticballsisnotuniform.Theplasticballsarenottrulyspherical.Anob

18、jectisthrownwithvelocityvfromtheedgeofacliffabovelevelground.Neglectairresistance.Inorderfortheobjecttotravelamaximumhorizontaldistancefromthecliffbeforehittingtheground,thethrowshouldbeatanangleOwithrespecttothehorizontalofgreaterthan60abovethehorizontalgreaterthan45butlessthan60abovethehorizontalgreaterthanzerobutlessthan45abovethehorizontalzerogreaterthanzerobutlessthan45belowthehorizontalAcartravelsforwardwithconstantvelocity.Itgoesoverasmallstone,whichgetsstuckinthegrooveofatire.Theinitialaccelerationofthestone,asitleavesthe