美国1998高中物理竞赛题及答案

1998PhysicsOlympiadpage1PhysicsOlympiadEntianonmultiplicandasuntpraeternecessitatem1998MULTIPLECHOICESCREENINGTEST30QUESTIONS—40MINUTESINSTRUCTIONSDONOTOPENTHISTESTUNTILYOUARETOLDTOBEGINThistestcontains30multiplechoicequestions.Youranswertoeachquestionmustbemarkedontheopticalmarkanswersheetthataccompaniesthetest.Onlytheboxesprecededbynumbers1through30aretobeusedontheanswersheet.Selectthesingleanswerthatprovidesthebestresponsetoeachquestion.PleasebesuretouseaNo.2pencilandcompletelyfilltheboxcorrespondingtoyourchoice.Ifyouchangeananswer,thepreviousmarkmustbecompletelyerased.Ahand-heldcalculatormaybeused.However,anymemorymustbeclearedofdataandprograms.Calculatorsmaynotbeshared.Yourgradeonthismultiplechoicetestwillbeyournumberofcorrectanswers.Thereisnopenaltyforguessing.Itistoyouradvantagetoanswereveryquestion.Thevaluesofsomepossiblyusefulconstantsaregivenbelow:massofelectronme=9.1x10-31kgmassofprotonmp=1.7x10-27kgelectronicchargee=1.6x10-19Cspeedoflightc=3.0x108m/sCoulomb'sconstantk=9.0x109N·m2/C2permittivityconstantε0=8.9x10-12C2/N·m2permeabilityconstantμ0=4¹x10-7T·m/AgravitationalconstantG=6.7x10-11N·m2/kg2massofEarthME=6.0x1024kgradiusofEarthRE=6.4x106mgravitationalfieldatEarth’ssurfaceg=9.8N/kgspeedofsound(20oC)vs=340m/sDONOTOPENTHISTESTUNTILYOUAREINSTRUCTEDTOBEGINCopyright©1998,AAPT1998PhysicsOlympiadpage21.Thegraphtotherightisaplotofpositionversustime.Forwhichlabeledregionisthevelocitypositiveandtheaccelerationnegative?A.AB.BC.CD.DE.E2.Achildleftherhomeandstartedwalkingataconstantvelocity.Afteratimeshestoppedforawhileandthencontinuedonwithavelocitygreaterthansheoriginallyhad.Allofasuddensheturnedaroundandwalkedveryquicklybackhome.Whichofthefollowinggraphsbestrepresentsthedistanceversustimegraphforherwalk?stE.stD.stC.stB.stA.3.Inarescueattempt,ahoveringhelicopterdropsalifepreservertoaswimmerbeingsweptdownstreambyarivercurrentofconstantvelocityv.Thehelicopterisataheightof9.8m.Theswimmeris6.0mupstreamfromapointdirectlyunderthehelicopterwhenthelifepreserverisreleased.Itlands2.0minfrontoftheswimmer.Howfastisthecurrentflowing?Neglectairresistance.A.13.7m/sB.9.8m/sC.6.3m/sD.2.8m/sE.2.4m/s4.Achildtossesaballdirectlyupward.ItstotaltimeintheairisT.ItsmaximumheightisH.WhatisitsheightafterithasbeenintheairatimeT/4?Neglectairresistance.A.(1/4)HB.(1/3)HC.(1/2)HD.(2/3)HE.(3/4)H5.Awhiffleballistossedstraightup,reachesahighestpoint,andfallsbackdown.Airresistanceisnotnegligible.Whichofthefollowingstatementsaretrue?I.Theball’sspeediszeroatthehighestpoint.II.Theball’saccelerationiszeroatthehighestpoint.III.Theballtakesalongertimetotraveluptothehighestpointthantofallbackdown.A.IonlyB.IIonlyC.I&IIonlyD.I&IIIonlyE.I,II,&IIIxtABCDE1998PhysicsOlympiadpage36.Apendulumisattachedtotheceilingofanelevatorcar.Whenthecarisparked,thependulumexhibitsaperiodof1.00s.Thecarnowbeginstotravelupwardwithanupwardaccelerationof2.3m/s2.Duringthispartofthemotion,whatwillbetheapproximateperiodofthependulum?A.0.80sB.0.90sC.1.00sD.1.10sE.1.20s7.TwoidenticalblocksofweightWareplacedoneontopoftheotherasshowntotheright.Theupperblockistiedtothewall.ThelowerblockispulledtotherightwithaforceF.Thecoefficientofstaticfrictionbetweenallsurfacesincontactisμ.WhatisthelargestforceFthatcanbeexertedbeforethelowerblockstartstoslip?A.μWB.(3/2)μWC.2μWD.(5/2)μWE.3μW8.Anobjectplacedonanequalarmbalancerequires12kgtobalanceit.Whenplacedonaspringscale,thescalereads120N.Everything(balance,scale,setofmasses,andtheobject)isnowtransportedtothemoonwherethegravitationalforceisone-sixththatonEarth.Thenewreadingsofthebalanceandthespringscale(respectively)are:A.12kg,20NB.12kg,120NC.12kg,720ND.2kg,20NE.2kg,120N9.Alargespoolofropeliesontheground.Seethediagramtotheright.Theend,labeledX,ispulledadistanceSinthehorizontaldirection.Thespoolrollswithoutslipping.Thedistancethespool’scenterofmassmovesisA.2SB.SC.S/2D.S/3E.S/410.AirtrackcarZofmass1.5kgapproachesandcollideswithairtrackcarRofmass2.0kg.Seetheaccompanyingdiagram.CarRhasaspringattachedtoitandisinitiallyatrest.Whentheseparationbetweenthecarshasreachedaminimum,then:A.carRisstillatrest.B.carZhascometorest.C.bothcarshavethesamekineticenergy.D.bothcarshavethesamemomentum.E.thekineticenergyofthesystemhasreachedaminimum.FWWXZR1998PhysicsOlympiadpage411.Twoiceskaters,a200lbmananda120lbwoman,areinitiallyhuggingonafrictionlesslevelicesurface.Tensecondsaftertheypushofffromeachother,theyare8.0mapart.Howfarhasthewomanmovedinthattime?A.8.0mB.6.5mC.5.0mD.4.0mE.3.0m12.Thediagramtotherightshowsthevelocity-timegraphfortwomassesRandSthatcollidedelastically.Whichofthefollowingstatementsistrue?I.RandSmovedinthesamedirectionafterthecollision.II.ThevelocitiesofRandSwereequalatthemid-timeofthecollision.III.ThemassofSwasgreaterthanthemassofR.A.IonlyB.IIonlyC.I&IIonlyD.II&IIIonlyE.I,II,&IIIQuestions13and14refertothemotionoftwoblocksalongafrictionlessleveltrack.Block#1(massm1)isinitiallymovingwithspeedvo.Itcollideswithandstickstoaninitiallystationaryblock(#2)ofmassm2=9m1.13.Whatisthespeedofthetwoblocksafterthecollision?A.voB.(9/10)voC.(8/9)voD.(1/9)voE.(1/10)v