西南交大 大学物理 英文 试题 答案no.a1-2.11348895new

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1、UniversityPhysicsAINo.2MotioninTwoandThreeDimensionsClassNumberNameI．ChoosetheCorrectAnswer1.Anobjectmovesinthexyplanewithanaccelerationthathasapositivexcomponent.Attimert=0theobjecthasavelocitygivenbyv=3iˆ+0ˆj.Whatcanbeconcludedabouttheycomponentoftheacceleration?(D)(A)Theyc

2、omponentmustbepositiveandconstant.(B)Theycomponentmustbenegativeandconstant.(C)Theycomponentmustbezero.(D)Nothingatallcanbeconcludedabouttheycomponent.dvxdvySolution:Accordingtothedefinitionoftheaccelerationcomponentsa=anda=,xydtdtifweonlyknowtheinitialvelocityoftheobject,not

3、hingatallcanbeconcludedabouttheycomponent.r2.Anobjectmoveswithaconstantaccelerationa.Whichofthefollowingexpressionarealsoconstant?(B)rrrrdv2d(v/v)dvd(v)(A).(B).(C).(D).dtdtdtdtvvdvSolution:Accordingtotherelationoftheaccelerationandthevelocitya=,weknowthedtvvelocityvisvarywith

4、time.Themagnitudeandthedirectionofthevelocitymaynotbeconstant,vvdvtherefore(A),(C)and(D)arenotcorrected.Asa==constant,answer(B)isthecorrectdtanswer.r3.Anobjectislaunchedintotheairwithaninitialvelocitygivenbyv=(4.9iˆ+9.8ˆj)m/s.0Ignoreairresistance.Atthehighestpointthemagnitude

5、ofthevelocityis(B)2222(A)0.(B)4.9m/s.(C)9.8m/s.(D)(4.9)+(9.8)m/s.Solution:Theycomponentofthevelocityiszeroatthehighestpoint,andthexcomponentofthevelocityisr4.9m/s,thusthevelocityisv=(4.9iˆ)m/s,themagnitudeis4.9m/s.II.FillingtheBlanks1.Agypsymothcaterpillar(Porthetriadispar)in

6、chesalongacrookedbranchtoatastyoakleaf,wriggling15yTreetrunkcmhorizontallyandthen30cmalongasectionofthe30cmobranchinclinedat30tothehorizontalasshowninFigure15cmo30x1.(a)Theinitialpositionvectors−0.15iˆandthefinal0Branchpositionvectors0.153iˆ+0.15ˆjofthecaterpillarinFig.1SIuni

7、tsusingthecrookinthebranchastheoriginforasetofhorizontalandverticalcoordinateaxes.(b)Ifthecaterpillartraversesthedistanceduring1.0min,itsaveragespeedis0.0075m/s,itsaveragevelocityis0.0068iˆ+0.0025ˆj(m/s),andthemagnitudeofitsaveragevelocityis−37.24×10m/s.Solution:v(a)Thecoordi

8、natesystemisshowninfigure.Theinitialpositionvectorisr=−0.15iˆ,andthe