1.A0.25gfleasitsonadiscatadistanceof4cmfromthecenterofthedisc.ifthediscrotatesat67rpmandthefleaisjustabletomaintainitspositionwithoutsliding,determinethecoefficientofstaticfrictionbetweenthefleaandthedisc|小学英语问答-字典翻译问答网

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问题描述：

2.SnoopyisflyinghisvintagewarplaneinloopthelooppathchasingtheredBaron.hisinstrumentstellshimthattheplaneislevel(atthebottomoftheloop)andtravellingataspeedof180km/h.heissittingonabathroomscale,andnotesthatitreadsfourtimesthenormalforceofgravityonhim.whatistheradiusoftheloop?

3.Asanindicationofthesizeofthesun'sgravitationalpullonearth,carryouttheroughcalculationsthatfollow.supposethatthesun'sgravitationalattractioncouldbereplacedbyasteelwire,runningfromthesuntotheearth,withthewire'stensionholdingtheearthinitsorbit.goodsteelhasabreakingstressof5.0x10^8N/m^2ofcrosssectionarea.

a)calculatethecross-sectionareaofwirethatcouldjustholdtheearthinitsorbit.

b)calculatethecorrespondingwirediameter.

4.Bylookingatdistancegalaxies,astronnomershaveconcludethatoursolarsystemiscirclingthecenterofourgalaxie.thehubofthisgalaxieislacatedabout2.7x10^20mfromoursun,andoursuncirclesthecenteraboutevery200millionyears.weassumethatoursunisattractedbyalargenumberofstarsatthehubofthegalaxy,andthatthesuniskeptinorbitbythegaravitationalattractionofthesestars.

a)calculatethetotalmasssofthestaratthehubofourgalaxy

b)basedonanaveragesizestarofmass2.0x10^30kg,determinetheapproximatenumberofsuchstarsatthehub

请把公示写清楚点不要只给我答案

可以用以下公示：

Fnet=mxa

Fc=mxac

Fg=mg

Fg=Gm1m2/d^2

脑子不太好使呵呵帮下忙

陆永忠回答：

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　　1.A0.25gfleasitsonadiscatadistanceof4cmfromthecenterofthedisc.ifthediscrotatesat67rpmandthefleaisjustabletomaintainitspositionwithoutsliding,determinethecoefficientofstaticfrictionbetweenthefleaandthediscthatenablesthefleatomaintainitsuniformcircularmotion. 　　A)calculatetheforceappliedtotheflea 　　F=ma=mω^2*r=m*r*(2π/T)^2,whereT=1/n,nistherpm(i.e.67) 　　B)thencalculatethestaticcoefficientoftheflea. 　　TheformulaforthestaticcoefficientisgivenbyF(inNewtons)=mgx 　　wherem=massinkg,g=9.81&xisthestaticcoefficient 　　2.楼上已经解释的很清楚了　　3.Asanindicationofthesizeofthesun'sgravitationalpullonearth,carryouttheroughcalculationsthatfollow.supposethatthesun'sgravitationalattractioncouldbereplacedbyasteelwire,runningfromthesuntotheearth,withthewire'stensionholdingtheearthinitsorbit.goodsteelhasabreakingstressof5.0x10^8N/m^2ofcrosssectionarea. 　　a)calculatethecross-sectionareaofwirethatcouldjustholdtheearthinitsorbit. 　　b)calculatethecorrespondingwirediameter. 　　A)Fg=Gm1m2/d^2 　　whichistheforcethatthewiremusthold.SoG(ofsun)*massofsun*MassofEarth*/thedistancesquared. 　　(thisistheequationyougave). 　　Thatforcedividedbythebreakingstressperarea(5.0x10^8)isequaltotheareaofthewire. 　　B)Area=pi*r^2.&diameter=2r.simpleenough. 　　4.Bylookingatdistancegalaxies,astronomershaveconcludethatoursolarsystemiscirclingthecenterofourgalaxy.thehubofthisgalaxyislocatedabout2.7x10^20mfromoursun,andoursuncirclesthecenteraboutevery200millionyears.weassumethatoursunisattractedbyalargenumberofstarsatthehubofthegalaxy,andthatthesuniskeptinorbitbythegravitationalattractionofthesestars. 　　a)calculatethetotalmassofthestaratthehubofourgalaxy 　　Fg=Gm1m2/d^2 　　Assumethatthesunfollowsacircularpathway,thedistancethesuntravelsiscalculatedwiththeradiusgiven(2.7x10^20m).Andthespeedcanbecalculated.Knowingthatwhileinorbit,asatelliteisalwaysaccelerating.F=ma=mω^2*r=m*r*(2π/T)^2,hence,youhavetheforceandacceleration. 　　Next,youcancalculatem1bysubstitutinginforallvalues. 　　b)basedonanaveragesizestarofmass2.0x10^30kg,determinetheapproximatenumberofsuchstarsatthehub 　　m1/massperstar. 　　Messagemeifyoudon'tunderstandthesolution.HowImisshighschoolphysics.^__^