美国1999高中物理竞赛题及答案

1999PhysicsOlympiad11999AAPTPHYSICSOLYMPIADEntianonmultiplicandasuntpraeternecessitatem1999MULTIPLECHOICESCREENINGTEST30QUESTIONS-40MINUTESINSTRUCTIONSDONOTOPENTHISTESTUNTILYOUARETOLDTOBEGINThistestcontains30multiplechoicequestions.Youranswertoeachquestionmustbemarkedontheopticalmarkanswersheetthataccompaniesthetest.Onlytheboxesprecededbynumbers1through30aretobeusedontheanswersheet.Selectthesingleanswerthatprovidesthebestresponsetoeachquestion.PleasebesuretouseaNo.2pencilandcompletelyfilltheboxcorrespondingtoyourchoice.Ifyouchangeananswer,thepreviousmarkmustbecompletelyerased.Ahand-heldcalculatormaybeused.However,anymemorymustbeclearedofdataandprograms.Calculatorsarenottobeshared.Yourscoreonthismultiplechoicetestwillbeyournumberofcorrectanswers.Thereisnopenaltyforguessing.Itistoyouradvantagetoanswereveryquestion.Thevaluesofsomepossiblyusefulconstantsaregivenbelow:massofelectronme=9.1x10-31kgmassofprotonmp=1.7x10-27kgelectronicchargee=1.6x10-19Cspeedoflightc=3.0x108m/sCoulomb’sconstantk=9.0x109N.m2/C2permittivityconstante0=8.9x10-12C2/N.m2permeabilityconstantm0=4πx10-7T.m/AgravitationalconstantG=6.7x10-11N.m2/kg2massofEarthME=6.0x1024kgradiusofEarthRE=6.4x106mgravitationalfieldg=9.8N/kgspeedofsound(200C)vs=340m/sDONOTOPENTHISTESTUNTILYOUARETOLDTOBEGINCopyright1999,AmericanAssociationofPhysicsTeachers.1999PhysicsOlympiad21.Atruckdrivertravelsthree-fourthsthedistanceofhisrunatonevelocity(v)andthencompleteshisrunatonehalfhisoriginalvelocity(½v).Whatwasthetrucker’saveragespeedforthetrip?[A]0.85v[B]0.80v[C]0.75v[D]0.70v[E]0.65v2.HerculesandAjaxhorizontallypushinthesamedirectionona1200kgcrate.Herculespusheswithaforceof500newtonsandAjaxpusheswithaforceof300newtons.Ifafrictionalforceprovides200newtonsofresistance,whatistheaccelerationofthecrate?[A]1.3m/s2[B]1.0m/s2[C]0.87m/s2[D]0.75m/s2[E]0.5m/s23.Auniform2kgcylinderrestsonalaboratorycartasshown.Thecoefficientofstaticfrictionbetweenthecylinderandthecartis0.5.Ifthecylinderis4cmindiameterand10cminheight,whichofthefollowingisclosesttotheminimumaccelerationofthecartneededtocausethecylindertotipover?[A]2m/s2[B]4m/s2[C]5m/s2[D]6m/s2[E]Thecylinderwouldslideatalloftheseaccelerations.4.Atrightisagraphofthedistancevs.timeforcarmovingalongaroad.Accordingthegraph,atwhichofthefollowingtimeswouldtheautomobilehavebeenacceleratingpositively?[A]0,20,38,&60min.[B]5,12,29,&35min.[C]5,29,&57min.[D]12,35,&41min.[E]atalltimesfrom0to60min.5.Aballwhichisthrownupwardnearthesurfaceoftheearthwithavelocityof50m/swillcometorestabout5secondslater.IftheballwerethrownupwiththesamevelocityonPlanetX,after5secondsitwouldstillbemovingupwardsatnearly31m/s.ThemagnitudeofthegravitationalfieldnearthesurfaceofPlanetXiswhatfractionofthegravitationalfieldnearthesurfaceoftheearth?[A]0.16[B]0.39[C]0.53[D]0.63[E]1.591999PhysicsOlympiad36.Twolightplasticshoppingbagsofnegligiblemassareplaced2metersapart.Eachbagcontains15oranges.If10orangesweremovedfromonebagtotheother,thegravitationalforcebetweenthetwobagswould[A]increaseto3/2theoriginalvalue.[B]decreaseto2/5theoriginalvalue.[C]increaseto5/3theoriginalvalue.[D]decreaseto5/9theoriginalvalue.[E]notchange.7.IfanetforceFappliedtoanobjectofmassmwillproduceanaccelerationofa,whatisthemassofasecondobjectwhichacceleratesat5awhenacteduponbyanetforceof2F?[A](2/5)m[B]2m[C](5/2)m[D]5m[E]10m8.Alargebeachballisdroppedfromtheceilingofaschoolgymnasiumtothefloorabout10metersbelow.Whichofthefollowinggraphswouldbestrepresentitsvelocityasafunctionoftime?[A][B][C][D][E]9.Adriverina1500kgsportscarwishestopassaslowmovingtruckonatwolaneroad.Whatistheaveragepowerinwattsrequiredtoacceleratethesportscarfrom20m/sto40m/sin3seconds?[A]10,000[B]20,000[C]100,000[D]300,000[E]400,00010.A40kgmassisattachedtoahorizontalspringwithaconstantof500N/m.Ifthemassrestsonafrictionllesshorizontalsurface,whatisthetotalenergyofthissystemwhensetintosimpleharmonicmotionbyanoriginaldisplacementof0.2meters?[A]10J[B]20J[C]50J[D]4000J[E]100,000J1999PhysicsOlympiad411.Twoskatersonafrictionlesspondpushapartfromoneanother.OneskaterhasamassMmuchgreaterthanthemassmofthesecondskater.Aftersometimethetwoskatersareadistancedapart.Howfarhasthelighterskatermovedfromheroriginalposition?[A]d[B]dMmFHGIKJ[C]dmMFHGIKJ[D]dmMm+FHGIKJ[E]dMmM+FHGIKJ12.Giventhethreemassesasshowninthediagram,ifthecoefficientofkineticfrictionbetweenthelargemass(m2)andthetableisμ,whatwouldbetheupwardaccelerationofthesmallmass(m3)?Themassandfrictionofthecordsandpulleysaresmallenoughtoproduceanegligibleeffectonthesystem.[A]mgmmm1123++bg[B]gmmmmm12123+++mbgbg[C]gmmmmmmm123123++--bgbg[D]gmmmmmmm123123--++bgbg[E]gmmmmmm123123--++mbgbg13.Anobjectwithamassof2kilogramsisacceleratedfromrest.Thegraphatrightshowsthemagnitudeofthenetforceinnewtonsasafunctionoftimeinseconds.Att=4secondstheobject’svelocitywouldhavebeenclosesttowhichofthefollowing:[A]2.2m/s[B]3.5m/s[C]5.8m/s[D]7.0m/s[E]11.5m/s14.Athinringofmassmandradiusrrollsacrossthefloorwithavelocityv.Whichofthefollowingwouldbethebestestimateofthering’stotalkineticenergyasitrollsacrossthefloor?[A]mv2[B]122mv[C]14mv2[D