Answers to exam-style questionsTopic 17a9.8=8820All numerical answers are quoted to 2 s.f.m=900kg[1 Thickness of sheet=7mm/160=0.044mm=4.4×10-5m69=33303.7N/kg[9002 a systematic or zero error8aAnswers in italicsb 9swingsc time=5.9-0.5=5.4sDensity/g/Volume/cm3cm3d time for 1 swing=5.4/9=0.60sSubstance Mass/gA540200=540/2003 Scalars:mass,kinetic energy,time=2.7Vectors:velocity.weight,accelerationB67.5=675/1.51.5=454 Resultant velocity =12+42=4.1m/stan=4,0=76 north of due east=250×0.52500.5=125b C only1009aV=140-20=120cm3[1].mass=246-15080=96g[1】.p=m/V=0.80g/cm3[60bV=200-140=60cm3[1].mass=411-24640(2.75g/cm3 exactly)2010 Liquid B floats on liquid AEither calculate both densities p=m/V:liquidtime/sAp=1.1 g/cm3 [1].liquid Bp=0.92g/cm3Or state as both liquids have same mass,sinceB has greater volume [1],it has lower density[1b average speed=5m/s11 a Graph A shows a directly proportionaltotal time taken20relationship.[1]This could be a spring.c Line B as shown in imageGraph B shows a non-linear relationship.[1]6 a Speed in m/s ony-axis [1]time in s onx-axis [1]The load/force required stretching the materialline plotted as shown belowchanges with extension Below 5cm,a largeforce is needed per unit extension:beyond 5cm201the force required decreases then begins to15increase again.[speed/10Graph C is linear until 20cm [1]then non-linear [1]m/s(Supplemental students-this could be a springstretched beyond its limit of proportionality.)005101520time/s=25N/mx0.2b Distance travelled =area under the graph [1]c Limit of proportionality occurs at 40cm.[=210m.[12012 a There is no resultant force/resultant force isillegaltotal timezero.6=11 m/s to 2 s.f.[10.5m/s exactly).b The resultant force is in the opposite directionto the movement of the car.[d=1.3 m/s2 to 2s.f.[1.25m/s2 exactly)13 a resultant force 1800-(980+500)=320N [1]toc△12upwards2]b The rocket will accelerate [1]upwards.thispagMike Folland and Catherine Jones 2022Answers to exam-style questionscm=W_980=100kg[122aW=Fd=25×2=50J[89.8b[acceleration=F=320-3.2m/s?W=Fd-147×1.5=220J[exact answer220.5J月[1)m10023aThere is no air pollution [1],but the other typesThe rocket accelerates upwards at 3.2m/s2[of pollution are a matter of opinion.Some people14a450×1.2=540Nmconsider that the landscape can be spoiled[visual pollution),but others like to look at windb To balance there must be no resultant moment.turbines.Wind turbines create noise pollution540=1.5×Wthat upsets some people.The scientific evidenceW=360Nabout whether or not noise is a real problemis unclear.[1]Over a whole year,a well-chosen15 Clockwise moment =1.8x 300=540Nmlocation will give a reliably predictable amountAnticlockwise moment =1.4x 400=560Nmof energy.[1]But,day-to-day,the amount of windTo balance clockwise moment,must increase byis very uncertain [1],so wind farms need to be20Nm.part of a complete energy strategy for a country,20Nm=2×Ftogether with other types of electricity generationF=10N downb Wind energy is renewable.[1]Wind energy willnot be used up/kinetic energy of the wind is16 A Bunsen burner has a base with a large area;transferred to the turbine.[1]it is also heavier at the bottom so the centre ofc e.g.Energy from hydroelectric dams is from agravity is low.[1renewable source.17 a momentum before collisione.g.Energy from fossil/nuclear fuel is from a=6000×6+10000×2non-renewable source=36000+20000=56000kgm/s24 efficiency=useful power output×100%=56000kgm/s [1]so momentum is conservedtotal power input432,×100%=40%1080=128000J[1After=h×16000×3.52=98000J[1]Reduced25 work done on load =40x 1.4=56Jby 30000J.Not conserved.efficiencyuseful energy outputc Energy is transferred to the thermal store of thetotal energy inputsurroundings.[1]=560N[2△0.02×100%=80%[2]7019 Answers in italics:1 mark for each correct answerAE96000EnergyEnergy26aP==800W2×60[2store at theEnergystore at thestart thattransferend that750×15DevicedecreasesprocessincreasesbP==375W[230battery-chemicalelectricalkineticpowered fan energyworkingenergy27power input =work done each second Fd=mgdrollermechanicalkinetic=24×9.8×60=14112J/scoasterpotentialenergyworkingenergypower output 11 000W[elastic energymechanicalkineticabedcatapultworkingenergytotal power input20 a gravitational potential energykinetic energy[1]elastic (strain)energy11000×100%=78%14112c△E,=mg△h=60×9.8×20=11760JdEk=2mv2=h×60×152=6750J28 The head of the drawing pin has a much largerelastic energy=11760J-6750J=5000Jsurface area than the pointed end.[1]This means for[exact answer=5010J月the same force applied the pressure on the head is21Ek=hmv2=h×0.060×122=4.32Jless than the pressure at the point.[E=△E4.32=0.06×9.8×hh=7.3mCambridge IGCSE Physics Study and Revision Guide Third EditionAnswers to exam-style questions29area=0.8×1.3-1.04m2[8 a stays the same [1]because the ice receivesthermal energy but its temperature cannot rise=4700Paabove0°C[A1.04decreases [1]because the water transfers30 a The pressure increases with depth.[1]The bottomthermal energy to the ice so its temperatureof the dam is thicker so that it is strong enoughdecreases[to withstand the pressurec increases[p=hpg=78×1000×9.8=760000Pad stays the same[9 Difference:evaporation takes place at all liquidtemperatures;boiling takes place at a definiteTopic 2temperature.Difference:evaporation takes place on the surface:a The momentum of the gas particle changes[1]boiling takes place throughout the liquid;which requires a force on the particle exertedDifference:evaporation takes place without energyby the wallinput:continuous boiling requires continuousenergy input.b The total force [1]due to collisions of all theSimilarity:substance changes state from liquid toparticles divided by the total area of the walls isgas.the pressure on the walls of the container.Similarity:energy is required to break bonds2 a pressure decreasesbetween moleculesb kinetic energy of particles stays the same10373K[1].100°Cc rate of collisions per unit area decreases11 The strips will curl with the bronze on the outsided totalforce per unit area decreases[1]because bronze expands more than invar3B12 a energy=200×5×60[1]=60000J4 a increases [1]because the speed and kineticb specific heat capacity=energy of the particles is higher at higherenergy/(mass x temperature rise)temperatureb increases [1]because the particles are movingc mass=energy/(specific heat capacityxfaster and so move between the walls in ashorter time=0.14kgc increases [1]because more collisions causegreater change of momentum and greater13 Metals have free electrons.[1]These electrons moveforce[1through the metal transferring thermal energy.1BGases and liquids rely on the secondary mechanismof conduction by collisions between molecules.pollen particles on the14 a conduction [1],there is solid contact betweensurface of watertheir hand and the metal gatecontainerb convection [1],the water molecules move pasttheir hand removing thermal energyc infrared radiation [1],no medium is requiredfor the transfer of thermal energywater[115 a infrared [1]radiationb probe XMicroscope drawn in viable positionb The pollen particles are seen to move [1]c temperature decreases [1],the rate of thermalrandomly.energy radiation received from the Sun becomesc Moving water molecules [1]collide randomly withless [1],temperature of the probe falls until itpollen particles and cause them to move.emits thermal energy at the same rate as it isreceivedtyillegal16 mainly convection [1],the radiator heats the air6next to it causing its density to fall so it risesP1=260Pasmall amount of radiation [1],the radiator is atinitial pressure =160Pa above atmospherica higher temperature than the room so thermalpressure[1energy is radiated to the roomtocopythispagMike Folland and Catherine Jones 2022