西南交大 大学物理 英文 试题 答案no.a1-3.11348896

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1、UniversityPhysicsAINo.3Newton’sLawsofMotionClassNumberNameI．ChoosetheCorrectAnswer1.Whichstatementismostcorrect?(C)(A)Uniformcircularmotioncausesaconstantforcetowardthecenter.(B)Uniformcircularmotioniscausedbyaconstantforcetowardthecenter.(C)Uniformcircularmotioniscausedbyaconstantmagnitu

2、denetforcetowardthecenter.(D)Uniformcircularmotioniscausedbyaconstantmagnitudenetforceawaythecenter.Solution:Foruniformcircularmotion,thespeedortheangularspeedoftheparticleisaconstant.2v2AccordingtoF=ma=m=mωr,ccrthemagnitudeoftheforcetowardthecentershouldbeconstant.r2.SupposethenetforceFo

3、nanobjectisanonzeroconstant.Whichofthefollowingcouldalsobeconstant?(D)(A)Position.(B)Speed.(C)Velocity.(D)Acceleration.rrSolution:AccordingtoNewton’ssecondlawF=ma,theansweris(D).3.WhichofthegraphinFigure1bestshowsthevelocity-timegraphforanobjectlaunchedverticallyintotheairwhenairresistanc

4、eisgivenbyD=bv?Thedashedlineshowsthevelocitygraphiftherewasnoairresistance.(B)vvvvtttt(A)(B)(C)(D)Solution:Duringthecourseoftheobjectmovesup,theaccelerationoftheobjectbythinkingaboutairresistanceislargerthanthatnoairresistance,itimpliesthatthetangentofthegraphshouldbelargerthanthatnoairre

5、sistance.Thusweremovetheanswer(D).Duringthecourseoftheobjectmovesdown,whent→∞,a→0,v→constant.Thinkingaboutthis,therightansweris(B)II.FillingtheBlanksr21.A2.50kgsystemhasanaccelerationa=(4.00m/s)iˆ.Oneoftheforcesactingonthesystemis(3.00N)iˆ−(6.00N)ˆj.Isthisthetotalforceonthesystem?No.Ifnot

6、,theotherforceactingonthesystemis7.00iˆ+6.00ˆj(N).vrSolution:ThetotalforceisF=ma=2.5×4.00iˆ=10.0iˆ(N)vvTheotherforceisF=F−(3.00iˆ−6.00ˆj)=7.00iˆ+6.00ˆj(N)total2.Twomasses,m1andm2,hangoveranidealpulleyandthesystemisfreetomove(seeFigure1).SuchanarrangementiscalledanAtwood’smachine.Therm−m21

7、magnitudeoftheaccelerationaofthesystemoftwomassesisg.m+m122m1m2m1Themagnitudeofthetensioninthecordisg.m+mm212Fig.1Solution:Thesecondlawforcediagramsoftwomassareshowninfigure.Assumethemassm2movesdownward.ApplyNewton’ssecondlawofmotion,wehave⎧m2g−T=m2a⎨vvT−mg=ma⎩11TTS