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如图所示，竖直平面内有一半径为R的光滑圆弧轨道，其末端与足够长的水平轨道平滑连接，一质量为m的小球P从圆弧轨道顶端由静止开始沿轨道下滑，在圆弧轨道末端与质量为2m的静止小球Q发生对心碰撞．小球P、Q...
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高三下学期物理《》真题及答案
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如图所示AB是竖直面内的四分之一圆弧形光滑轨道下端B.与水平直轨道相切.一个小物块自A.点由静止开始
固定的光滑圆弧轨道ABC处在竖直平面内圆轨道半径为R.半径OA处于水平OB处于竖直方向如图所示一个小
如图所示竖直平面内的3/4圆弧形光滑轨道半径为R.A.端与圆心O.等高AD为水平面B.点在圆弧的最高
如图所示在竖直平面内有一半径为R.的圆弧轨道半径OA水平OB竖直一个质量为m的小球自
的正上方P.点由静止开始自由下落,小球沿轨道到达最高点
时恰好对轨道没有压力.已知AP=2R,重力加速度为g,则小球从P.到B.的运动过程中( )
A.重力做功2mgR B.机械能减少mgR
合外力做功mgR
克服摩擦力做功
mgR
如图所示在竖直平面内有一半径为R.的圆弧轨道半径OA水平OB竖直一个质量为m的小球自A.的正上方P.
如图所示水平光滑地面上停放着一辆小车左侧靠在竖直墙壁上小车的四分之一圆弧轨道AB是光滑的在最低点B.
如图所示水平地面上固定着一辆小车左侧靠在竖直墙壁上小车的四分之一圆弧轨道AB是光滑的在最低点B.与水
如图所示在一固定的竖直光滑圆弧轨道内部的最低点静止有一个可视为质点的小球已知地球表面的重力加速度为g
2015年·延边州一模如图所示在竖直平面内半径为R的四分之一圆弧轨道AB水平轨道BC与斜面CD平滑连
如图所示水平光滑地面上停放着一辆小车左侧靠在竖直墙壁上小车的四分之一圆弧轨道AB是光滑的在最低点B.
如图所示半径可变的四分之一光滑圆弧轨道置于竖直平面内轨道的末端B.处切线水平现将一小物体从轨道顶端
处由静止释放。若保持圆心的位置不变,改变圆弧轨道的半径(不超过圆心离地的高度)。半径越大,小物体 ( )
A.落地时的速度越大
平抛的水平位移越大
到圆弧轨道最低点时加速度越大
落地时的速度与竖直方向的夹角越大
如图所示竖直平面内有一光滑圆弧轨道其半径为R.平台与轨道的最高点等高一小球从平台边缘的A.处水平射出
如图所示在竖直平面内有一半径为R.的圆弧轨道半径OA水平OB竖直一个质量为m的小球自
的正上方P.点由静止开始自由下落，小球沿轨道到达最高点
时恰好对轨道没有压力己知AP=2R，重力加速度为g，则小球从P.到B.的运动过程中( ) A.重力做功2mgR B.机械能减少mgR
合外力做功mgR
克服摩擦力做功
如图所示放置在光滑水平面上的长木板其上表面与左侧竖直平面内的光滑圆弧轨道底端B.相切木板长度l=1.
15分如图所示竖直平面内有一圆弧形光滑轨道圆弧半径为R.AD为水平面A.端与圆心等高B.点在圆心的正
如图所示AB是竖直面内的四分之一圆弧形光滑轨道下端B与水平直轨道相切.一个小物块自A点由静止开始沿轨
如图所示在距水平地面高为h处有一半径为R.的1/4圆弧轨道圆弧轨道位于竖直平面内轨道光滑且末端水平在
如图所示竖直平面内有一个四分之三圆弧形光滑轨道圆弧半径为R.AD为水平面A.端与圆心等高B.点在圆心
如图所示在竖直平面内有一半径为R.的圆弧轨道半径OA水平OB竖直一个质量为m的小球自A.的正上方P.
如图所示竖直平面内有一个四分之三圆弧形光滑轨道圆弧半径为R.AD为水平面A.端与圆心等高B.点在圆心
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IworkinamarketinLondonjustattheweekends﹣﹣﹣I'vegotasecond﹣handbookstoreandonedayI1getmystorereadywhenanoldladycameupandstartedlookingatthebooks.ShestartedchattingandtellingmehowsheusedtoliveinthatpartofLondonand2muchithadchangedsinceshe'dlastbeeninthearea.WhileweweretalkingIputoutabook3coverwasalittleoldandshepickeditup.OhGrimm'sFairyTalesshesaidIhadacopyofthis4Iwasachild. Shebeganflickingthrough翻阅itandIcarriedonlayingoutthebooksandwhenIlookedupshewasjuststandingthere5shakeandshe'dgone6completewhite.But…but…thisismyactualbookshesaid.Lookit'sgotmynameJoaninit.Thenshetoldmehowthere'dbeenaterriblefirewhileherfamilywereaway7holidayandthehousehadbeenburnttotheground.Shethoughtallherbelongings8destroy.Shepulledoutherpurse9buythebookfrommebutIstoppedher.Nono…pleaseacceptit10agift﹣it'ssuchawonderfulstory.
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某老小区建成时间较早没有集中供暖随着人们生活水平的日益提高热力公司决定在此小区加装暖气该小区的物业公司统计了近五年截止2018年年底小区居民有意向加装暖气的户数得到如下数据 Ⅰ若有意向加装暖气的户数y与年份编号x满足线性相关关系求y与x的线性回归方程并预测截至2019年年底该小区有多少户居民有意向加装暖气 Ⅱ2018年年底郑州市民生工程决定对老旧小区加装暖气进行补贴该小区分到120个名额物业公司决定在2019年度采用网络竞拍的方式分配名额竞拍方案如下①截至2018年年底已登记在册的居民拥有竞拍资格②每户至多申请一个名额由户主在竞拍网站上提出申请并给出每平方米的心理期望报价③根据物价部门的规定每平方米的初装价格不得超过300元④申请阶段截止后将所有申请居民的报价自高到低排列排在前120位的业主以其报价成交⑤若最后出现并列的报价则认为申请时问在前的居民得到名额为预测本次竞拍的成交最低价物业公司随机抽取了有竞拍资格的50位居民进行调查统计了他们的拟报竞价得到如图所示的频率分布直方图 1求所抽取的居民中拟报竞价不低于成本价180元的人数 2如果所有符合条件的居民均参与竞拍请你利用样本估计总体的思想预测至少需要报价多少元才能获得名额结果取整数 参考公式对于一组数据x1y1x2y2x3y3…xnyn其回归直线＝x+的斜率和截距的最小二乘估计分别为＝＝﹣
BecautiousofFridaythe13th!Manypeoplethinkthedayisunlucky.1fortunethere'sonlyoneFridaythe13ththisyear.Asthelegendgoesyoushouldtrynot2breakanymirrorswalkunderaladderorevenspillanysalt.Why?Researcherssay3istoughtofindouthowthetraditioncameintobeing.Manybelieveithas4religionorigins.IntheChristianfaiththerewereguestsattablefortheLastSupperwhichwasheldthedaybeforetheFriday5Jesusdied.NowFridaythe13thhasbecomeaculturalwonder.ManyAmericansavoidthenumber13alltogether6includehotelroomsandairplaneseatassignments.Itevencostscoupleslesstogetmarriedontheday.Therearemanyother7explainbehindthelucklessday.SimonBronneraprofessorofAmericanstudiesatPennsylvaniaStateUniversity8believeFridaythe13thisawayforpeopletopintheirbadlucktoacertaincause.Thefactshouldbe9there'snothingspecialaboutthenumberitself.Afterallthenumber1310considertobeluckyinsomecountrieslikeItaly.
假设你是红星中学高三学生李华你写信建议你的美国朋友George参加中国日报ChinaDaily专门为外国人举办的2018最美中国AmazingChina手机摄影大赛. 信的内容包括1.作品内容要求 2.提交时间和方式 3.表示愿意提供帮助. 注意1.词数不少于100 2.开头和结尾已给出不计入总词数. DearGeorge I'mlookingforwardtoyourreply.﹣﹣﹣﹣ Yours LiHua
若定义在R上的函数fx满足fx＝﹣fx﹣4且当﹣1≤x≤1时fx＝﹣2﹣x+1则f2019＝
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DonateYourUsedBooks Whenitcomestodonatingusedbookslookbeyondyourlocallibraryorthriftstorethereareplentyofincredibleorganizationsmakingadifferenceintheworldthroughthepowerofbooks.Herearesomeofthebest. Sendusedbookstodeployedsoldiers AgreatwaytohonorandsupportourtroopsistodonatebookstoBooksforSoldiers.Thisnon﹣profitallowsuserstosignintoadatabaseandreceivebookrequestsfromindividualsoldiers.Mail﹣calldaysaresomeofthemosthighlyexpectedeventsforthem.1. Givethemtothenation'spoorestcommunities ReadertoReader'simpacthasbeenincrediblywide﹣reachingandimpressive.2.Theprogramspecificallybenefitsthenation'spoorestcommunitiesfrominner﹣cityschoolsandNativeAmericanReservationstoimpoverishedruraltowns.ReadertoReaderhasdonatedover2millionbookstorebuildschoollibrariesdestroyedbyHurricaneSandyandothernaturaldisasterslikefiresandtornadoes.Bydonatingyourbookshereyou'llmakeahugeimpactinAmerica'sstrugglingcities. Helpprisonersgetaneducation BooksforPrisonersisanon﹣profitstudentorganizationbasedattheUniversityofCaliforniaSanDiego.Thisincredibleprogramdonatesbooksandresourcestoinmatesfromalloverthecountry.Individualinmateswritetotheorganizationoftenrequestingspecificbooksdictionariesandtextbooksfortheirstudies.BooksforPrisonersinturnsendstherequestedmaterialsinthehopesoffurtheringtheireducationandhelpingtoturntheirlivesaround.3.Soyoucanhelpmaketheirgoalsarealitybydonatingyourusedbooks. 4 PajamaProgramsupportschildreninunstableanduncertainlivingsituations.ThisNewYork﹣basednonprofitgenerouslydonatesbooksandpajamastokidslivinginsheltersgrouphomesandtemporaryhousingfacilities.5.HoweverbydonatingyourbookstoPajamaProgramyoucanhelpkidsfeelsafeimportantandloved. A.Sendthemtohomelesschildren B.Educationiskeytoabetterlifeforthem C.Soyoucanreallybrightenatroop'sdaywithyourliterarygift. D.Nightfallistheweakesttimeforthesechildren E.Whenthebooksarrivetheygotothosewhoneedthemmost. F.Soyourdonationscanalsogotoaschoolcountrylibraryprisonlibraryornursinghome. G.Thischarityisdevotedtobringingbookstounder﹣resourcedschoolsandpubliclibrariesacrossAmerica.
设函数fx＝|x+3|+|2x﹣a|﹣1a∈R． Ⅰ若不等式fx+|x+3|≥3对任意的x∈R成立求实数a的取值范围 Ⅱ当a＞﹣6时函数φx＝2|x+3|﹣x﹣fx有三个不同的零点求a的取值范围．
已知函数fx＝若∀x1x2∈﹣12＞0则实数m的取值范围为．
函数y＝4+3的最大值为
已知函数fx＝如果对任意t∈Rf3t2+2t+fk2﹣2t2＜0恒成立则满足条件的k的取值范围是．
已知b＜＜a＜1则下列不等式中一定成立的是
若关于x的不等式|ax﹣3|＜7的解集为{x|﹣5＜x＜2}则a的值为
设复数z＝a+bii为虚数单位ab∈R且＝b+i则复数z的模等于
若函数y＝6lnx的图象上各点的横坐标变为原来的λλ＞0倍纵坐标保持不变所得函数的图象与函数y＝﹣x+22+a图象上存在关于原点对称的点且a的最小值为1﹣3ln3则实数λ＝
函数fx的图象如图所示f'x是fx的导函数下列数值排序正确的是
设fx＝x3+3ax+a在区间01内有极小值点则实数a的取值范围为
OnNov24nearYellowstone'snortheastentranceSpitfireafemalegreywolfwasshotandkilledbyahunterassheapproachedagroupofcottages. ItwasalegalharvestAbbyNelsonawolfmanagementspecialistsaid.Thecircumstancesareobviouslyalittlebitharderforpeopletostomachbutthatpackhasshowedsignsofhabituation习惯.Theyjuststandthereandhavenofear.Wolfhunterscaneasilypicktheonetheywant. ThecarefreerelationthatsomeYellowstonewolveshavebuiltwithhumansisreportedlyattractiveforhunterswholookforaneasykill. InthewakeofyetanotherfamousYellowstonewolfmeetingaviolentendoutsidetheparkofficialsareactivelyrethinkinghowtomanagewildlifehabituation. SmithawolfbiologistforYellowstonesaysNowwe'rethinkingofpoundingthem.Parkofficialsmightusefireworksandpaintballorbeanbaggunswhentheyapproachhumansinthepark.Ifyougetclosetopeopleyou'regoingtogetattacked. Ifyouthinkthissoundscruelyou'renotalone.Seeingthesecreaturesfromtheroadsthatwindthroughtheparknotonlyallowstouriststowitnesssomethingamazingbutalsotoreconnectwithnatureinawaythatisbetterthananyconservationcampaign.Butthere'salsoagrowingsensethatthepresentpolicyofdoingnothingisn'tworkingmorewolveswillneedlesslydieandthebrokenrecordofhuntersscoringeasykillswillgoon. AsSmithaddsurgingpeopletokeepwolveswildwhenmeetingthemhalfwayisabigask.Stillhe'shopefultopreservetheworld'sbestplacetoobservefree﹣rangingwolvesit'sapolicychangethattouristscanbeinvolvedin..perhapsSpitfire'sdeathwillaccomplishsomegoodandwe'llallcometogethertodoabetterjobonmanagingcrowdsandroadsandwolvesinYellowstoneSmithsaid. 1WhatwasthemainreasonforthedeathofSpitfire? A.Wildlifehabituation B.Parkofficialscarelessness. C.Thenatureofgreywolves. D.Thecrueltyofthehunter 2Whatdoestheunderlinedwordpoundinginparagraph5probablymean? A.Greeting B.Protecting. C.Challenging D.Hitting. 3WhatdoesSmithexpectvisitorstodoinYellowstone? A.Bemorefriendlytowolves B.Avoidmeetinggreywolves. C.Keepawayfromwolves. D.Forcewolvesawayfromthem 4Whatisthemainideaofthetext? A.ThewolvesinYellowstoneareoutofcontrol B.Illegalwolf﹣huntinginYellowstoneisgoingon C.Yellowstoneconsidersattackingwolvestoprotectthem D.ThewolvesinYellowstonearelivinginharmonywithhumans.
己知偶函数y＝fx在﹣∞0上单调递增若a＝fb＝f2﹣1.2c＝f则
阅读下面短文根据所给情节进行续写使之构成一个完整的故事. WhenRyanfirstturnedupforMs.Rose'sclasshewaskindofnervousbecausehe'dheardMs.Rosecouldbearealmonstersometimes.ButasMs.Rosestartedwithanoverviewofwhatthey'dbedoingduringtheyearinapleasantvoiceshelookedniceenough.Thenwithamoreseriousoneshewarnedthestudentsthatshe'dbegivingthemhomeworkassignmentswhichwerenottobehandedinlateandtheyweretobecompletedfully.Noexcuse!Noextensions! Thatdaysheassignedtheclassitsfirsthomework.Theyhadtodoasheetofmathproblemsandreadashortstory.Itwasn'tdueuntilThursdaybutshesuggestedtheydoitimmediatelythatnight.Homeworkhasawayofpilingup.shesaidhereyesnarrowingslightly.ButtodaywasonlyMonday!TherewasplentyoftimeRyanthought. SowhenschoolwasoverRyanandhisfriendsranofftoplaybaseball.ExhaustedafterthegameheentertainedhimselfwithhisfavoriteTVshowleavinghishomeworkasideonhisdesk.DayspassedquicklyRyanwasfreeofworriesmostofthetimewhileMs.Rosejustoccasionallyremindedthemofthedeadlineandthatshewouldn'ttolerateanyonenothavingdoneit. Wednesdayafterdinnerhesuddenlyrealizedthathishomeworkwasduenextday.Heracedtohisdeskandwasgreetedwiththemostcuriousthing.Thepileofhomeworkreallyhadgrowntaller.Ohno!Whatwashegoingtodo?Itlookedasifthepapershadtoweredoverhimalmostsoaringuptotheceiling. Hereallyneededtogetstarted.Hedidalittlebithereandtherebuthekeptdistractedbyotherworkwaitingforhim.Finallyhecouldn'tevenlocatethehomeworkhe'dstartedwith.Frustratedhegaveupandwenttobed.Ryantossedandturnedallnightandhaddreamsofpapermountainsburyinghimalive. ThenextmorningwhenRyanenteredtheclassroomhefoundMs.Rosewaitingherfaceddarkwithrage.ObviouslyRyanwasn'ttheonlyonewhosufferedfromthemysteriouslygrowingassignments. 注意 1.所续写短文的词数应为150左右 2.至少使用5个短文中标有下划线的关键词语 3.续写部分分为两段每段的开头语已为你写好 4.续写完成后请用下划线标出你说使用的关键词语. Paragraph1 FailingtomeetthedeadlinethestudentshadtowatchasMs.Rosetransformedintotherealmonster. Paragraph2 WithasatisfiedsmileMs.Rosefinallyreleasedeveryonebutassignedtheclasssomeextrahomework.
已知函数且fm＝﹣2则fm﹣6＝
在直角坐标系xOy中直线C1x＝﹣3圆C2x﹣22+y﹣12＝1以坐标原点为极点x轴正半轴为极轴建立极坐标系 Ⅰ求C1C2的极坐标方程 Ⅱ若直线C3的极坐标方程为θ＝ρ∈R设C2C3的交点为AB求△C2AB的面积．
Atfirstglancethebusinessworldisnoplaceforyoungwomenasmyco﹣foundersandIhavebeentoldonmanyoccasions.Inspiteofthispessimisticviewofwomen'sopportunityinbusinesswethreecollege﹣agegirlwithzeroexperienceinbusinessstartedoffwithahighlyambitiousgoaltostartaseaweedfarminNorthCaliforniaandgrowasmuchseaweedaspossibletohelpreducecarbonemission排放andnutrientpollutionfromagriculturalsources. Inthebeginningourideaswereeitherignoredorscoffedbytheresearchersfromwhomwesoughthelpandadvice.Butwecarriedonwithourresearch﹣ifotherswouldn'tprovideusanswersweweren'tafraidtoworkthemoutourselves.Wediscoveredwhichspeciescouldgrowinwarmerwatersandwe'didentifiedpotentialmarketsintowhichweplannedtoselltheproducts.We'vespentthelasttwoyearssettingupthefirstseaweedfarminNCapplyingforapatent专利andcompetingwithfivefinalteamsinfrontoftheUnitedNationsfor﹩1million. Despitealloureffortsmanyindustryexpertsremainedunwillingtotakeusseriously.Butasoftenhappensinbusinessthesamecharacteristicswewereignoredforwereinrealityourbiggestcompetitiveadvantages.Ouragegaveusthestrengthtobouncebackfromfailureandourbackgroundasenvironmentalscientistsratherthanbusinesswomenhelpedusfindnewmarketingopportunities.Forevery10farmerswhoclaimednobodywouldeverwanttofeedtheircowsseaweedwefoundonewhowasinterested.Forevery15cosmeticsproducerswhorefusedtoanswerourcoldcallswestucktotheonewithaninterestingideaforseaweedlotion. Overthecourseofourearlybusinessdevelopmenteffortswehavehadaccesstoawealthofresourcesprogramsandindividualswhoworkconstantlytohelpussucceed.Bystayingfocusedonbringingourideastolightourteamhasdemonstratedthatentrepreneurship创业isexactlytherightplaceforthehopeful. 1Whatwasthemajorcausefortheirdifficultyinstartingbusiness? A.Theyarewomen. B.Theywereyoung. C.Theylackedexperience. D.Theysufferedprejudice. 2Whatdidtheydotomaketheirbusinesssuccessfulaccordingtothepassage? A.Theyexpandedtheirseaweedfarms. B.Theyexperimentedonseaweedspecies. C.Theygottheirproductofficiallyrecognized. D.TheyconsultedtheUnitedNations. 3Whatisthethirdparagraphmainlyabout? A.Howtheybenefitedfromtheirweaknesses. B.Howtheygotothersinterestedinseaweed. C.Howtheymadethemselvesmorecompetitive. D.Howtheyapproachedpotentialcustomers. 4Whatisthefollowingcanbebestdescribethethreewomen? A.Naiveandsimple﹣minded. B.Ambitiousandself﹣centered. C.Adventurousandpersistent. D.Stubbornandcourageous.
某同学根据一组xy的样本数据求出线性回归方程＝x+和相关系数r下列说法正确的是
在矩形ABCD中对角线AC分别与ABAD所成的角为αβ则sin2α+sin2β＝1在长方体ABCD﹣A1B1C1D1中对角线AC1与棱ABADAA1所成的角分别为α1α2α3与平面AC平面AB1平面AD1所成的角分别为β1β2β3则下列说法正确的是 ①sin2α1+sin2α2+sin2α3＝1 ②sin2α1+sin2α2+sin2α3＝2 ③cos2α1+cos2α2+cos2α3＝1 ④sin2β1+sin2β2+sin2β3＝1
Whatmakesagoodapology?Whatistherightwaytosaywe'resorrythatdoesn'tmerelyrelieveourguiltorgetusoutofhotwaterbutbestservesthepersonwehurt?Thereismoretosayingsorrythanjustsayingsorry.1Theyincludeexpressingregretexplainingwhatwentwrongacknowledgingresponsibilityofferingtorepairthesituationandrequestingforgiveness. Thatmayseemlikealottorememberbutacknowledgementofresponsibilityturnedouttobethemostimportantpiece.Ofcoursenotalltheruinedsituationsarecreatedequal.2Hereareafewkeytips. Haveperfecttiming.Didyoutotallyruinthesituation?Alittlecool﹣offtimecouldhelp.3.Butiftheotherpartyisangryatyourwrongdoingitmaybemoreeffectivetowaitbecausetheirangermaypreventthemfrombeingreceptivetoanapology.Waitingcanhelpyoutoo.Thebesttimetoapologizeiswhenonefeelsreadytosincerelyapologize. 4Expertsagreethatface﹣to﹣faceapologiesbeatphoned﹣ine﹣mailedorhandwrittenones.Facialexpressionsgesturesandthetoneofvoicehaveallbeenshowntobeimportantchannelsthatconveysincerity.AnyonecantypeIfeelreallyashamedbutifyousayitliveit'sobviouswhetherornotyoumeanit. Explaindon'texcuse.Becauseadmittingtobeingwrongispainfulandcanmakepeopleworriedthatthey'reabadpersontheyoftenwaterdowntheirapologywithexcuses.ExamplesincludeIcertainlyapologizeifIoffendedanyoneandI'msorrybutyoustartedit.Thatsortofapologyhasanameanon﹣apology.Itusestheformofanapologybutfollowsitupbyshifting﹣responsibilitytotheoffendedpersonImplyingheorsheistoosensitive.5Evenifyoudidsomethingcomparablylessimportantlikebeinglateallthetimeit'salwayskeytorememberthatwhileyou'retheoneapologizingit'snotaboutyouit'saboutthepersonyouhurtandwhattheyneednow. A.Letyourbodydothetalking. B.Thereareseveraltypesofapologies. C.Getreadytochangeyourfacialexpressions. D.SometimesanImmediateapologyiscalledfor. E.Don'timplythattheotherpersoniswrongtofeelupsetorangry. F.Infactastudyfoundthateffectiveapologieshavefivecomponents. G.Soyoumightneedtofine﹣tuneyourapologydependingonthecircumstances.
恩格尔系数Engel'sCoefficient是食品支出总额占个人消费支出总额的比重恩格尔系数越小消费结构越完整生活水平越高某学校社会调查小组得到如下数据 若y与x之间有线性相关关系某人年个人消费支出总额为2.6万元据此估计其恩格尔系数为． 参考数据＝4＝22.5 参考公式对于一组数据x1y1x2y2x3y3…xnyn其回归直线＝x+的斜率和截距的最小二乘估计分别为＝＝﹣
某校有ABCD四个社团其中学生甲乙丙丁四人在不同的四个社团中在被问及在哪个社团时甲说“我没有参加A和B社团”．乙说“我没有参加A和D社团”．丙说“我也没有参加A和D社团”．丁说“如果乙不参加B社团我就不参加A社团”．则参加B社团的人是
设函数fx＝a∈R Ⅰ若fx在x＝0处取得极值确定a的值并求此时曲线y＝fx在点1f1处的切线方程 Ⅱ若fx在[3+∞上为减函数求a的取值范围．
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A.重力做功2mgR B.机械能减少mgR 合外力做功mgR 克服摩擦力做功
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A.落地时的速度越大 平抛的水平位移越大 到圆弧轨道最低点时加速度越大 落地时的速度与竖直方向的夹角越大
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