Physics 6091 Sec 4 Prelim Paper 2 Markscheme 2021

DUNMANSECONDARYSCHOOLSECONDARY4EXPRESSPHYSICS6091PRELIMINARYEXAMINATION2021SUGGESTEDMARKSCHEME PAPER2–SECTIONA1(a) Thedifferencebetweenascalarquantityandavectorquantityisthatascalarquantityhasonlymagnitudewhereasavectorquantityhasbothmagnitudeanddirection. B1 1(b) Thevectorquantityisdisplacement/velocity/acceleration/moment. B11(c) 30°TB =400sin30°=200N (note:todeterminebasedondiagramandcanacceptmathscalculation) TC =400cos30°=346N (note:todeterminebasedondiagramandcanacceptmathscalculation) B1 B1 B1 2(a) Thegradientofthegraphincreaseswhichindicatesthatthevelocityisincreasing. B12(b) Terminalvelocity=(60–20)/(3.5–2.0)=27m/s(2sf) M1A12(c) Asitfallsfromrest,weightactsdownwards,thusresultantforceisactingdownwards.Asspeedincreases,airresistancealsoincreasesResultantforceactingdownwardsdecreasestozero B1B12(d) A1 3(a)(i) Fnet =ma4.0-0.80=2.0aa=1.6m/s 2 1.6= 𝑣 − 𝑢∆𝑡 M1

= 𝑣 − 05.0 v=8.0m/s A13(a)(i) SinceFnet =0whenFbalancesthefrictionalforceof0.8N,BasedonNewton’sSecondLaw,theaccelerationbecomeszero.BasedonNewton’sFirstLaw,theboxcontinuestomoveataconstantspeed(of8.0m/s)inthesamedirection. B1 B1 3(b) SinceFistheactionforceexertedbytheboyonthebox,theotherforce,F1,whichisequaltoFinmagnitude,butactingintheoppositedirectionofFisthereactionforcebytheboxactingontheboy.F1ispartoftheaction-reactionpairwithFbyNewton’sThirdLaw. B1B1 4(a)(i) kineticenergyatB=gravitationalpotentialenergyatA=mgh=50x10x(350/100)=1750J=1800J(2sf) M1A14(a)(ii) (½)mv 2 =1750 OR1800v=8.37m/s=8.4m/s(2sf) ORv=8.49=8.5m/s(2sf) M1A14(b)(i) energylostduetofriction=50x10x[(350–300)/100]=250J M1A14(b)(ii) workdoneagainstfrictionis250Jforcexdistance=250Jforce=250/15=16.7N=17N(2sf)[Note:itisokforthisanswernottohaveunitNandallowECFfrom4(b)(i)]] A1 5(a) Energymust beprovidedbyexternal sourcetoweakentheintermolecular forceofattractionORfortheliquidmoleculestogaininternalpotentialenergyintheliquidinorderforittobecomegas. B1 5(b) Total energylost =energylost bywater duringcooling+latent energylost duringfreezing =mc +mLf ∆θ =500(4.2)(30–0)+500(330)=228000J=230000J(2sf) M1M1A1 5(c) Theheatedwaterneartheheateratthebottomofthetankexpandsandrisesduetodecreaseddensity. Thecoolerwaterfromthetopsinksasithasahigherdensity. Thissetsupaconvectioncurrentuntilallwaterinthetankisheated. B1 B1

6(a) X1 andY1 orX2 andY2 B1 6(b) PA =PB 1.20xρA xg=0.76x13600xgρA =8613=8600kg/m 3 (2sf) M1A16(c) Whenthetapisopened,theliquidlevelsinbothtubeswill dropandachievethesameheight astheliquidsinthecontainers. B1 B1 7(a) Electronsaretransferredfromthepipetothefuelduringtherubbingaction. B17(b) Sparkmightjumpfromthechargedplaneandignitethefuelcausingexplosion. B1B17(c) Metalisanelectricalconductor(orhaslowresistance)whichwill allowelectronstoflowthroughit fromtheaeroplanetotheground. ORaeroplanetobeearthed. B1B1 8(a) Whentheswitchisclosed,currentwillflowthroughthecoilandtheironcorebecomesanelectromagnet.Theelectromagnet will inducemagnetismintheironbolt. Hence, theelectromagnetattractstheironbolt,causingittomovetotheleft,allowingthedoortobeopened. B1 B18(b) Increasethecurrent/increasethenumberofturnsonthecoil/movetheironcoreclosertotheironbolt. [Any2] Thechangesincreasethestrengthof theelectromagnet / Magneticfieldisstrongerclosertheelectromagnet(ifchangegivenistomoveironcoreclosertotheironbolt). B1 B1 8(c) Steelisapermanentmagnet,hencetheremightbeanissueforthesteelbolttocloseefficiently. Asthesteel bolt will remainattractedtotheironcorewhentheswitchisopened. B2 9(a) Whentheswitchisclosed,currentwillbeabletoflowthroughthemetalspokedwheelandsetupamagneticfieldaroundit.Thismagneticfieldwillinteractwiththemagneticfieldofthemagnet.Thiswillinteractionwillproduceaforcethatenablesthewheeltoturn. B1 B19(b) B1 9(c) Theforceexertedoneachspokewillcausethewheeltomoveacertaindistance.Havingaminimumof8spokeswillallowthenextspoketomaintainaclosecircuit. B1

ORtoallowmomentumforthewheeltorotatecontinuously. Paper 2–SECTIONB 10(a)(i) Highcurrentcausedoverheatingofthewire(P=I 2 Rheating)andwireAmelted. [Note:donotacceptvoltmeterrangeisfrom0to3.50Vandhencecouldnotmeasuremorethan3.50V.Underworkingconditions,thevoltmeterusedwouldbeableto.] B1 10(a)(ii) Thep.d.increasesproportionally/uniformly/constantly/linearlyascurrentincreases. B1 10(a)(iii) R=V/I=0.20/1.60=0.125=0.13Ω(2sf) A1 10(a)(iv) Workablecircuittovarycurrentandgetp.d.(e.g.useofrheostatorpotentiometerorvariablepowersupply) Correctlydrawncircuitsymbolsandconnectionswithruler Able to measure accurately current (ammeter) in wire and p.d.(voltmeter)acrosswire B1 B1 B1 10(a)(v) Approximately2.40A(samecurrentforseriesconnection).Sumofp.d.inbothwiresinseriesisabout 2.00V(wireA)+0.50V(wireB)=2.50V(drycell). B1 B110(b)(i) Strongwindcausescooling,reducingresistanceandhence,byV=IR,reducesthep.d.ORConductionofheatawayfromwirebythewindalsoleadstolowertemperature B1 10(b)(ii) Fig10.3isnowabletomeasurep.d.ofcurrentspreviouslynotmeasurableinFig.10.2ORFig.10.3showssmallerincreaseinp.d.ascurrentisincreasedthanFig.10.2 B1

11(a) Theearthwirewillconnectthemetalcasingtotheground/earth.Whenlivewiretouchesthemetalcasingitwilltriggerahighcurrentflowingtotheground/earth.Thishighcurrentwillcausethefusetomeltorblow,andthiswilldisconnectthehighvoltagetothecomputer.Thispreventstheuserfromelectricshock.(Note:donotacceptanswerifthestudentsexplainhowtheearthwireandfuseworkindependently.) B1 B1 B1 11(b) Athinnerwirewillheatupfasterduetohigherresistance. Thismightcausethewiretomeltandcausefirefromoccurring. B1 B111(c)(i) NS /NP =VS /VP NS =(15.0/240)x3600=225turns M1A111(c)(ii) For100%idealtransformer(zeroloss),IP xVP =IS xVS IP =(1.2x15.0)/240=0.075A(2sf) M1A1 11(c)(iii) IncreasethemagneticfieldstrengthbyconcentratingmagneticfieldlinesinsideitOREnsuresgoodmagneticfluxlinkagebetweenprimaryandsecondarycoil B1 12E(a) Airisopticallylessdensethanwater.Hence,speedoflightincreasesasitgetsfromwatertoair,causingthelighttobendawayfromthenormal B1B112E(b)(i) Angleofincidenceis0 o ORincidentrayliesalongthenormal.ORTherayhitsthesurfaceperpendicularly. B1 12E(b)(ii) n=1/sincc=sin -1 (1/1.56)=39.9 o A112E(b)(iii) Totalinternalreflectionwilloccur.Itisbecausetherayistravellingfromanopticallydensermediumtoalessdensemediumandtheangleofincidenceisgreaterthancriticalangle. B1 B1 12E(b)(iv) n=c/vv=c/n=3.0×10 8 /1.56v=1.92x10 8 m/s=1.9x10 8 m/s(2sf) M1A112E(b)(v) v=fxwavelengthwavelength=v/f=3.0x10 8 /6.5x10 14 M1

=4.62x10 -7 m=4.6x10 -7 m(2sf) A1 12O(a) Rateofflowofelectriccharge. B1 12O(b) 15VLDR50ΩV+- B1 12O(c)(i) I=V/R=15/(800+50)=0.0176A=0.018A(2sf) M1A112O(c)(ii) V=IR=800x0.0176 OR=800x0.018=14.1V=14V(2sf) =14.4V=14V(2sf) M1A112O(d) Voltmeterreadingwillslowlyincrease.Whenlightintensitydecreases,resistanceofLDRwillincreaseandhencethevoltagewillincrease. B1B112O(e) Voltmeterreadingwilldecrease.Withthelightintensityremainingconstant,resistanceofthecircuitwillincreasewiththe100Ωfixedresistor.Hence,currentinthecircuitwilldecrease.ThiswillcausethevoltageacrosstheLDRtodecrease. B1B1