MS P2

Sec4PurePhysicsPrelimMarkingScheme(Paper2)SectionAQn Answer Marks Remarks1(a) AccordingtoNewton’sFirstLaw,iftheforcesactingontheballarebalanced,theballwouldeitherbestationaryormovewithconstantvelocity,withoutanyacceleration./AccordingtoNewton’sSecondLaw,theaccelerationoftheballistheresultofaresultantforceactingontheball.Hence,theforcesactingontheballareunbalanced. 1 Acceptexplanationbasedoneither1 st or2 nd Law. Nomarkawardedforjuststating“unbalanced” 1(b) a=(v–u)/t2.0=v/2.0v=4.0m/s 11(c) s=(1/2)x2.0x4.0=4.0m 1 1 Ecfmarkscanbeawarded 2(a) ForceexertedbyManB=100x10–600=400N 12(b) LetthedistancebetweentheCGoftherodandmanAbed.TakingmomentaboutmanA,1000xd=400x6.0d=2.4m or TakingmomentabouttheCGoftherod,600xd=400x(6.0–d)d=2.4m 11 11 Ecfmarkscanbeawarded

3(a) PressureofgasB=120000–13600x10x0.08=109000Pa(3s.f.) 11 1markcanbeawardedforcalculatingthepressuredifference3(b) H1 woulddecreasewhileH2 wouldincrease.Blackisabetterabsorberofinfraredradiationthanwhite,hencethetemperatureofgasAwouldincreasefasterthanthatofgasB,resultinginanevengreaterpressuredifferencebetweengasAandgasB, 1 11 4(a) InitialGPE=finalKEmgh=(1/2)mv 2 300x10x8=(1/2)x300xv 2 v 2 =160v=12.6m/s 1 14(b) averageretardingforcex0.5=300x10x8averageretardingforce=48000N 115(a) Theairmoleculesinthecylinderareincontinuousandrandommotion,collidingwiththewallsofthecylinder.Theaverageforceexertedbytheairmoleculesonaunitareaofthecylindergivesrisetoapressureinthecylinder. 1 1 5(b) Thevolumeofairinthecylinderdecreases,causinganincreaseinthenumberofairmoleculesperunitvolume.Theairmoleculescollidewiththewallsofthecylindermorefrequently,causingtheforceexertedperunitareatoincrease,andhenceincreasingthepressureinthecylinder. 1 1 6(a) sin27°/sinr=1.50,r=17.6°angleofincidenceatCD=angleofreflection=angleofincidencebackatAB=18°angleofrefractionatAB=27° 1 1 FortheangleofincidenceatAB,accept26°to28°

6(b) sinc=1/1.50,c=41.8°TheangleofincidencewhenthelightrayleavesABis,whichissmallerthanthecriticalangle.Hence,totalinternalreflectiondoesnothappen. 11 7(a) Whentheobjectdistanceistwicethefocallengthofthelens,theimagedistanceisalsotwicethefocallengthofthelens.Fromthegraph,theobjectdistanceandimagedistanceareequalat3.0cm.Hence,thefocallengthofthelengthis3.0/2=1.5cm. 1 1 Nomarkawardedifnoinformationisquotedfromthegraph7(b) Whenobjectdistance=2.0cm,imagedistance=4.2cm.Magnification=4.2/2.0=2.1 11 Acceptraydiagrammethod 8(a) Accordingtothequestion,thecorksmoveupanddownasthewavepasses.Thisshowsthatthewaterparticlesmoveinadirectionperpendiculartothedirectionofthewaterwave,andthisisacharacteristicoftransversewave. 1 Nomarkawardedifnoinformationisquotedfromthequestion 8(b)(i)Speed=wavelength/period=8.0/0.50=16cm/sor0.16m/s 18(b)(ii) Sameamplitudeandperiod.WhenAisatthecrest,Bisatthetrough. 1 9(a) 1.Ultrasoundwavesarelongitudinalwaves,whilemicrowavesaretransversewaves.2.Ultrasoundwavescannottravelinvacuum,whilemicrowavescantravelinvacuum.3.Ultrasoundwavesrequireamediumtotravel,whilemicrowavesdonotrequireanymediumtotravel.4.Ultra