八下第二次月考试题
初中英语八年级下册月考试卷(含答案)

八年级英语下第二次月考试题班级:姓名:一、单项选择(40)( )1.Our parents often tell us not_______alone in the river in summer.A.swimB.to swimC.swimmingD.swam( )2.This story happened________ a small island.A.atB.onC.inD.of( )3.Uncle Ted was very rich. But now he has no place to_______.A.liveB.live onC.live inD.live with( )4.We found_______necessary to protect animals in danger.A.itB.thisC.thatD./( )5.You should_______smoking. It’s bad for your health.A.get upB.put upC.give upD.look up( )6. Mo Yan is one of ____most popular writers in the world. He was____honest boy when he was child.A.a; aB.a; anC.the; aD.the; an( )7 .The old man was _______angry _______ say a word.A. so, thatB. as, asC. too, toD. very, to( )8. Why _______home tomorrow?A.not goB.not goingC.not to goD.didn’t go( )9.I _________ some mo ney from him, but I’ll _______ it to him in a few days.A.borrow, returnB.lend, borrowC.borrow, keepD.borrow, lend ( )10.It was _________ exciting news for all the students.A.aB.anC.theD. /( )11. I am much better _________ Chinese _________ our teachers’ help.A.in, atB.at, inC.at, withD.with, with( )12._______ high school students in a poor mountain village is a difficult job.A.TeachingB.TeachC.TeachesD.Teachers( )13. Mother couldn’t find her ring. So she wanted to know _________.A.where it isB.where it wasC.where is heD.she was where ( )14.We_____ go on a picnic if it_____rain tomorrow.A.don’t, isn’tB.don’t, stopC. will, doesn’tD.aren’t, doesn’t ( )15.If you don’t want to go swimming, I ______.A.won’t, tooB.also won’tC.won’t, eitherD.won’t , neither ( )16. He was_____ tired ___he couldn’t go on working.A.too…toB.such…thatC.so…thatD.to o…that( )17.What an _______ story! I am much _________ in it.A.interested, interestingB.interesting, interestedC.interesting, interestingD.interested, interested( )18.My life will be ______ than it is now.A.more betterB.much goodC.much betterD.many better( )19.I ______to Hong Kong twice since I came to China 3 years ago .A.wentB.goC.have goneD.have been( ) 20. He is ______ a friendly man that people miss him very much .A.soB.suchC.themD. /( )21.Mother used to__the song“Where’s time going?”.Now she is used to____it.A.hating, listenB.hated, listened toC.hate, listening toD.hating, listening ( )22.Tony studies very ______. He often does his homework until 10:30p.m., but his brother Tom______ does homework.A. hardly, hardlyB. hard, hardlyC. hardly, hardD.hard, hard( )23.You eat _______ junk food. I think you need________vegetables.A.too much, muchB. too many, manyC. too much, lots ofD. too many, lot ( )24. The driver saw an old man _______ on the side of the road .A lie y C. lying D. to lie( )25.How kind you are! You always do what you can____ others.A. helpB. helpingC. helpsD. to help( )26. He _____ lots of money to the people in trouble _______.A.gave out; help them outB. gave away; to help them outC. put out; to help them outD. gave away; to help out them( )27. Could you give me a hand? I want to___the map on the wall.A. put upB. look upC. set upD. mix up( )28 .They need to come______ a good idea.A. on withB. up toC. on toD. up with( )29. When I came home, I ___________ my father ___________ a newspaper.A. find, readB. found, readingC. found, readsD. find, reading ( )30 .Could you please ______ me such boring questions? I’m tired.A. not askB. not to askC. not askingD. don’t ask( )31. I want ______ cr eam cake. It’s delicious.A. otherB. anotherC. the otherD. others( )32.—I’m sorry I ______my bag at home.—You did that last week. Never forget ______ it to school next time.A. forget, to takeB. forget, to bringC. left, to takeD. left, to bring ( )33. The cleaner said, “ __ things we do, __ environment we’ll have” .A. More, betterB. The more, the betterC. Fewer, The lessD. The fewer, better ( )34.Which is _____, German, maths or science?A. more interestingB. the most interestingC. interestingD. the interesting ( )35 .My headteacher saw her ______up some rubbish while he ______ by .A. pick, was passingB.picking, was passingC.was picking, was passingD.picking, passed( )36. The number seventy-eight thousand six hundred and forty-five can be written like this _______A.78,123B. 68,123C.78,645D.78,465( )37. What ____ you ______ at this time yesterday?A. did; doB. are; doingC. were; doingD. did, did( )38. Lin Tao is as ______ as Zhang Hua.A. strongB. strongerC. the strongestD. strongest ( )39. There are five ________ people in the city.A. millionsB. million ofC. millionD. millions of ( )40._______ students in our school enjoy listening to music.A. A number ofB. A number offC. The number ofD. The numbers of二、完形填空(10)One day, Peter had a fight with one of his classmates. Then he went to his grandfather and told him his story ____41___.“He is really bad,”the boy said,“and I 42 him.”The grandfather s aid,“43 me tell you a story. When I was a boy, I too, sometimes hated others for what they did.”As Peter 44 carefully, the grandfather went on.“There are always two tigers inside my he art. One is 45 and kind. He gets on well 46 everything around him. But 47 is bad and unfriendly. Even the smallest thing will make him angry. He fights with everyone all the time, and for no reason. He can’t think carefully 48 he always hates others. It is difficult to live with these two tigers inside my heart. They both try to control me.”Peter looked into h is grandfather’s 49 and asked,“ 50 tiger always controls you, Grandfather?”The old man said slowly and seriously,“The one that I feed. I always feed the good and kind tiger, so I never hate others and seldom(很少)get angry now.”( )41.A.happily B.friendly C.hardly D.angrily( )42.A.love B.hate C.know D.enjoy( )43.A.Make B.Help C.Let D.Ask( )44.A.saw B.felt C.talked D.listened( )45.A.good B.bad zy D.quiet( )46.A.at B.on C.with D.about( )47.A.other B.others C.another D.the other( )48.A.because B.though C.before D.but( )49.A.eyes B.ears C.nose D.mouth( )50.A.Who B.Which C.Where D.When三、阅读理解(30)AOnce there lived an old man. He liked gold better than anything else in the world. He often said, “If I have enough gold, I will be the happiest man in the world.”One day when he was traveling in the desert, the old man lost his way. He was very hungry and thirsty, but there were only rocks and sand around him. Just then, he found a bag lying on the sand. He hoped he would find water and food in it. He took up the bag and opened it. He saw that the bag was full of gold. He was so sad that he threw away the bag and began crying.Now, the old man knew that there was something better than gold in the world. ( )51. The old man liked ____ best before he traveled in the desert.A. foodB. bagsC. goldD. drinks( )52. When he lost his way, he wanted to get _________.A. some food and waterB. some rocks and sandC. bags full of goldD. some food and sand( )53. What did he do with the bag?A. He didn’t take it up.B. He brought it home.C. He threw it away.D. He picked it up.( )54. The old man did not become the happiest man when he got the bag of goldbecause ______.A. the bag was too smallB. the gold wasn’t hisC. he was very hungry and thirstD. he didn’t like gold a ny more( )55. In the end, the old man knew that gold was _________ in the world.A. the best thingB. not the best thing C .better than anything D. not hisBThere was a pilot and four people in a small plane. Suddenly there was something wrong with the machine while it was flying in the air. The smoke was everywhere in the plane. The pilot told the people there were only four parachutes(降落伞). They all became worried and started to make excuses.“I must go and m end the machine,” said the pilot, taking one of the parachutes. There was nothing he could do,so he jumped out.The first person stood up. “I’m a doctor”, he said. “I help peopl e live longer and I save lives.” He also took a parachute and jumped out.The next p erson said, “I must have p parachute. I am a very clever person. I have to go to an important sport match. I know I’ll win the game because I’ll be the cleverest person t here.” He picked up a backpack and jumped out.Two men were left—an old businessman and a young mountain climber. By this time the plane was going down fast. The businessman said, “Young man, I am old but you’re still young. You take the last parachute.”The young mountain climber smiled. “Don’t worry,” he said, “We can both jump to safety because there are still two parachutes. Just now the clever person jumped out with my backpack.”( )56. All the people became worried because ___.A. they coul dn’t find the parachutesB. they saw the pilot jump out firstC. something was wrong with the plane and one of them might dieD. there was too much smoke and they couldn’t jump out from the plane ( )57. The clever man jumped out with ___.A. a parachuteB. nothingC. the backpack of the climber’sD. two parachutes ( )58. All the people thought of themselves except ____.A. the pilotB. the clever manC. the doctorD. the businessman ( )59. From the story we know _____ would be dead.A. the clever manB. the businessmanC. the pilotD. the doctor ( )60. ____ was a kind-hearted man.A. The pilotB. The mountain climber.C.The businessmanD. The doctorC判断正误,正确的写A,错误的写B.Two friends were walking through the desert. They had an argument, the first friend slapped (一记耳光) the other in the face. The other friend was hurt, but only wrote in the sand: “Today my best friend slapped me in the face.”They kept walking, until found a lake. They decided to cool off and swim. The other friend started going down in the lake, but his friend saved him. After he came back to life, he wrote on a stone: “Today my best friend saved me.” The friend, who slapped and saved his friend, asked him: “After I hurt you, you wrote in the sand, and now, you wrote on the stone. Why?” The other friend answered: “When someone hurts us, we should write down in sand, when the winds of time and forgiveness(宽恕) can blow it. But when someone does something good for us, we must write it on the stone. No wind can blow it away.”( )61. The two friends were walking in the forest.( )62. They were going to cool and swim in the lake.( )63. The other friend wrote sentences on the stone every time.( )64. The winds of time and forgiveness can blow the words in the sand.( )65. In fact, they were real friends.四、根据句意和提示写出正确的单词(8)66.To our ___________(使我们惊讶的是), we found the owner of the lost dog.67.The________(感觉)of helping others makes me _______(觉得)happy.68.They went to the mountain to look for ___________ (财富).69.They didn’t achieve great ___________ (succeed) in life.70.People’s liv ing ____________(状况) were very poor in China in the past.71.The old bike ___________(提醒) me of my grandmother. has the largest _____________(人口) in the world.五、用所给词的适当形式填空(7)73. They couldn’t help ____________(cry) when they saw their parents.74. It was interesting _____ (see) so many places of interest from all over the world.75.One of ___________(beautiful) cities in China is Kunming.76. There are some students __________(lead) us to the forest park.77.Let’s go to Zhangjiajie to enjoy the _________(natural) .78.How long has your mother __________(teach) math at this school ?79.Do you know the girl ______ (call) Mary?六.句型转换(10分)80.He has already finished the homework.(改为否定句)He finished the homework .81.Tom is taller than any other boy in his class.(改为同义句)Tom is in his class.82.She has been a teacher for two years.(就画线部分提问)she been a teacher?83.He has been to an English-speaking country.(改为一般疑问句)he an English-speaking country?84.His sister cleans the room.(改为现在完成时)His sister the room.七、补全对话(5)A. Could I invite my friends to my birthday party on Saturday, Mom?B. Of course! 85 ____ ___.A. Yeah, Um…86 ________.B. What for?A. 87_______.B. I am shopping tomorrow. And I can buy some drinks and snacks for you.A. Oh, good. Thank you, Mom.B. You’re welcome. Oh, could you clean your room?A. 88_______.B. You need to clean it again for your party.A. Ok, but I need to do my homework first.B. That’s right. After you finish your homework, let’s clean the room. I cansweep the floor and do the dishes.A. 89_______.B. Yes, sure.八、作文(10)动物是人类的好朋友,没有动物,人类也不能生存,但现在很多动物濒临灭绝,请你就如何帮助动物提出建议。
辽宁省沈阳市和平区峥嵘中学2021-2022学年八年级下学期第二次月考数学试题(含答案解析)

辽宁省沈阳市和平区峥嵘中学2021-2022学年八年级下学期第二次月考数学试题学校:___________姓名:___________班级:___________考号:___________一、单选题1.观察如图所示的图形,绕着它的中心旋转120°后能与自身重合有()A .1个B .2个C .3个D .4个2.下面是四位同学解方程过程中去分母的一步,其中正确的是()A .2+x=x ﹣1B .2﹣x=1C .2+x=1﹣x D .2﹣x=x ﹣13.若分式3a ba 中的,ab 的值同时扩大到原来的3倍,则分式的值()A .是原来的3倍B .是原来的127C .是原来的19D .是原来的134.如图,在四边形ABCD 中,AD ∥BC ,∠BCD =90°,将四边形ABCD 沿AB 方向平移得到四边形A 'B 'C 'D ',BC 与C 'D '相交于点E ,若BC =8,CE =3,C 'E =2,则阴影部分的面积为()A .B .13C .D .265.已知在正方形的网格中,每个小方格的边长都相等,A ,B 两点在小方格的顶点上,位置如图所示,则以A ,B 为顶点的网格平行四边形的个数为()A .6B .8C .10D .126.新能源汽车环保节能,越来越受到消费者的喜爱.各种品牌相继投放市场.一汽贸公司经销某品牌新能源汽车.去年销售总额为5000万元,今年1~5月份,每辆车的销售价格比去年降低1万元.销售数量与去年一整年的相同.销售总额比去年一整年的少20%,今年1~5月份每辆车的销售价格是多少万元?设今年1~5月份每辆车的销售价格为x 万元.根据题意,列方程正确的是()A .50005000(120%)1x x-=+B .50005000(120%)1x x +=+C .50005000(120%)1x x-=-D .50005000(120%)1x x+=-7.如图,在ABC 中,ABC ∠和ACB ∠的平分线相交于点O ,过点O 作EF BC ∥交AB 于E ,交AC 于F ,过点O 作OD AC ⊥于D ,下列四个结论:①EF BE CF =+;②1902BOC A ∠=+∠︒;③点O 到ABC 各边的距离相等;④设,OD m AE AF n =+=,则AEF S mn =△.其中正确的结论是()A .①②③B .①②④C .②③④D .①③④8.如图,在正方形ABCD 中,点E ,F 分别在BC ,CD 上,AE =AF ,AC 与EF 相交于点G .下列结论:①AC 垂直平分EF ;②BE +DF =EF ;③当∠DAF =15°时,△AEF 为等边三角形;④当∠EAF =60°时,12ABE CEF S S =△△.其中正确的是()A .①③B .②④C .①③④D .②③④二、填空题9.若分式222x-+的值为0,则x 的值是______.10.若不等式组01x m x m ->⎧⎨-<⎩的解集中每一个x 值均不在25x ≤≤的范围内,则m 的取值范围是______.11.在平行四边形ABCD 中,∠A =30°,AD =BD =4,则平行四边形ABCD 的面积等于______________.12.如图,过边长为5的等边ABC 的边AB 上一点P ,作PE AC ⊥于E ,Q 为BC 延长线上一点,当PA CQ =时,连PQ 交AC 边于D ,则DE 的长为_____.13.如图,正方形ABCD 和正方形EFCG 的边长分别为3和1,点F 、G 分别在边,BC CD 上,P 为AE 的中点,连接PG ,则PG 的长为_________.三、解答题14.在A ,B 两地间仅有一条长为360千米的笔直公路,若甲,乙两车分别从A 、B 两地同时出发,匀速前往终点B ,A 两地,乙车速度是甲车速度的34倍,乙车比甲车晚到90分钟,求乙车每小时行驶多少千米?15.如图,ABC 和BDE △都是等腰直角三角形,90ACB DBE ∠=∠=︒,连接CD ,以CA ,CD 为邻边作CAFD Y ,连接CE ,BF .(1)如图1,当D 在BC 边上时,请直接写出CE 与BF 的关系;(2)如图2,将图1中的BDE △绕点B 顺时针旋转到图2的位置,其他条件不变,(1)中的结论是否成立?若成立,请给予证明;若不存在,请说明理由;(3)若3AC =,2BD =,将图1中的BDE △绕点B 顺时针旋转一周,当BD 与直线BC 夹角为30°时,请直接写出CE 的值.16.如图①,点E 为正方形ABCD 内一点,∠AEB =90°,将Rt △ABE 绕点B 按顺时针方向旋转90°,得到△CBE '(点A 的对应点为点C ).延长AE 交CE '于点F ,连接DE .猜想证明:(1)四边形BE 'FE 的形状是______;(2)如图②,若DA =DE ,请猜想线段CF 与FE 的数量关系并加以证明;(3)如图①,若AB =15,CF =3,求DE 的长.参考答案:1.B【分析】根据旋转的性质,对题中图形进行分析,判定正确选项.【详解】解∶①旋转120°后,图形可以与原来的位置重合,故正确;②旋转120°后,图形无法与原来的位置重合,故错误;③旋转120°后,图形无法与原来的位置重合,故错误;④旋转120°后,图形与原来的位置重合,故正确.故选∶B .【点睛】本题考查图形的旋转与重合,理解旋转图形的定义是解决本题的关键.2.D【详解】解:方程的两边同乘(x ﹣1),即可得2﹣x=x ﹣1.故选:D .3.C【分析】根据分式的基本性质即可求出答案.【详解】原式3333a 3b a b 1a b(3a)9a 9a +++===⨯;故选C .【点睛】本题考查分式的基本性质,解题的关键是熟练运用分式的基本性质,本题属于基础题型.4.B【分析】利用平移的性质得到B ′C ′=BC =8,BC ∥B ′C ′,CD ∥C ′D ′,S 梯形ABCD =S 梯形A ′B ′C ′D ′,然后根据S 阴影部分=S 梯形BB ′C ′E 进行计算.【详解】解:∵四边形ABCD 沿AB 方向平移得到四边形A 'B 'C 'D ',∴B ′C ′=BC =8,BC ∥B ′C ′,CD ∥C ′D ′,S 梯形ABCD =S 梯形A ′B ′C ′D ′,∴C ′D ′⊥BE ,∴S 阴影部分=S 梯形BB ′C ′E =12(8﹣3+8)×2=13.故选:B .【点睛】本题考查了平移的性质:把一个图形整体沿某一直线方向移动,会得到一个新的图形,新图形与原图形的形状和大小完全相同;新图形中的每一点,都是由原图形中的某一点移动后得到的,这两个点是对应点.连接各组对应点的线段平行且相等.5.D【详解】分析:根据平行四边形的定义:两组对边平行的四边形是平行四边形,显然图中以A 、B 为顶点的网格平行四边形的个数为12个,分以AB 为边和以AB 为对角线两种思路求解.详解:如图所示,根据平行四边形的定义,则以AB 为边的网格平行四边形有6个,以AB 为对角线的网格平行四边形有6个,则共有12个.故选D.点睛:本题考查了平行四边形的判定,此题要能够根据平行四边形的定义,分别以AB 为边或对角线找到所有的平行四边形.6.A【分析】首先根据所设今年每辆车的价格,可表示出去年的价格,同样根据销售总额的关系可表示出今年的销售总额,然后再根据去年和今年1~5月份销售汽车的数量相同建立方程即可得解.【详解】∵今年1~5月份每辆车的销售价格为x 万元,∴去年每辆车的销售价格为(x+1)万元,则有()5000120%50001x x-=+故选A.【点睛】此题主要考查分式方程的应用,解题的关键是找出题中去年和今年的关系.7.A【分析】根据角平分线的定义和三角形的内角和即可对②进行判断;根据平行线的性质和角平分线的定义可得,EBO EOB FCO COF ∠=∠∠=∠,再根据等角对等边即得,BE EO OF CF ==,进而可对①进行判断;过O 作OM AB ⊥于M ,作ON BC ⊥于N ,连接OA ,可得ON OD OM m ===,可得12AEF AOE AOF S S S mn =+=即可对④进行判断;根据角平分线的性质即可对③进行判断.【详解】解:∵在ABC 中,ABC ∠和ACB ∠的平分线相交于点O ,∴11,,18022OBC ABC OCB ACB A ABC ACB ∠=∠∠=∠∠+∠+∠=︒,∴1902OBC OCB A ∠+∠=︒-∠,∴()1180902BOC OBC OCB A ∠=︒-∠+∠=︒+∠;故②正确;∵在ABC 中,ABC ∠和ACB ∠的平分线相交于点O ,∴,OBC OBE OCB OCF ∠=∠∠=∠,∵EF BC ∥,∴,OBC EOB OCB FOC ∠=∠∠=∠,∴,EOB OBE FOC OCF ∠=∠∠=∠,∴,BE OE CF OF ==,∴EF OE OF BE CF =+=+,故①正确;过点O 作OM AB ⊥于M ,作ON BC ⊥于N ,连接OA ,∵在ABC 中,ABC ∠和ACB ∠的平分线相交于点O ,∴ON OD OM m ===,∴()11112222AEF AOE AOF S S S AE OM AF OD OD AE AF mn =+=⋅+⋅=⋅+=△△△;故④错误;∵在ABC 中,ABC ∠和ACB ∠的平分线相交于点O ,∴点O 到ABC 各边的距离相等,故③正确.故选:A .【点睛】本题考查了平行线的性质、等腰三角形的判定、三角形的内角和定理和角平分线的性质,属于基础题型,熟练掌握角平分线的性质等基本知识是解题关键.8.C【分析】①通过条件可以得出△ABE ≌△ADF ,从而得出∠BAE =∠DAF ,BE =DF ,由正方形的性质就可以得出EC =FC ,就可以得出AC 垂直平分EF ,②设BC =x ,CE =y ,由勾股定理就可以得出EF 与x 、y 的关系,表示出BE 与EF ,即可判断BE +DF 与EF 关系不确定;③当∠DAF =15°时,可计算出∠EAF =60°,即可判断△EAF 为等边三角形,④当∠EAF=60°时,设EC =x ,BE =y ,由勾股定理就可以得出x 与y 的关系,表示出BE 与EF ,利用三角形的面积公式分别表示出CEF S △和ABE S ,再通过比较大小就可以得出结论.【详解】解:①四边形ABCD 是正方形,∴AB =AD ,∠B =∠D =90°.在Rt △ABE 和Rt △ADF 中,AE AFAB AD =⎧⎨=⎩,∴Rt △ABE ≌Rt △ADF (HL ),∴BE =DF ,∵BC =CD ,∴BC ﹣BE =CD ﹣DF ,即CE =CF ,∵AE =AF ,∴AC 垂直平分EF .故①正确;②设BC =a ,CE =y ,则BE =DF =a -y ,∴BE +DF =2(a ﹣y ),EF y ,∴BE +DF 与EF 关系不确定,只有当y =(2)a 时成立,故②错误;③当∠DAF =15°时,∵Rt △ABE ≌Rt △ADF ,∴∠DAF =∠BAE =15°,∴∠EAF =90°﹣2×15°=60°,又∵AE =AF∴△AEF 为等边三角形.故③正确;④当∠EAF =60°时,则△AEF 是等边三角形,设EC =x ,BE =y ,则CF =x ,∴AB =BC =x +y ,22222EF CE CF x =+=,∴222AE x =,∵222AB BE AE +=,即()2222x y y x =++,∴()22x y x y =+,∵21122CEF S CE CF x =⋅=V ,()12ABE AB B y S E x y =⋅=+ ,∴12ABE CEF S S =△△.故④正确.综上所述,正确的有①③④,故选:C .【点睛】本题属于四边形综合题,是中考填空题或选择题的压轴题,考查了正方形的性质的运用,全等三角形的判定及性质的运用,勾股定理的运用,等边三角形的性质的运用,三角形的面积公式的运用,解答本题时运用勾股定理的性质是解题的关键.9.2【分析】根据分式值为0的条件解答即可.【详解】∵分式222xx x-+的值为0,∴22020x x x ⎧-=⎨+≠⎩,∴202x x x =±⎧⎨≠≠-⎩,,∴2x =.故答案为:2.【点睛】本题考查分式值为0的条件,解一元二次方程.掌握分式值为0的条件:分子为0,分母不为0是解题关键.10.1m ≤或5m ≥【分析】分别求出每一个不等式的解集,根据口诀:同大取大、同小取小、大小小大中间找、大大小小无解来确定不等式组的解集,再结合解集中任意一个x 的值都不在25x ≤≤的范围内可得答案.【详解】解:01x m x m ->⎧⎨-<⎩①②,解不等式①,得x >m ,解不等式②,得1x m <+,所以不等式组的解集是1m x m <<+,不等式组01x m x m ->⎧⎨-<⎩的解集中每一个x 值均不在25x ≤≤的范围内,12∴+≤或5mm≥,m≥,解得:1m£或5m≥,即m的取值范围是1m£或5m≥.故答案为:1m£或5【点睛】本题考查的是解一元一次不等式组,正确求出每一个不等式解集是基础,熟知“同大取大;同小取小;大小小大中间找;大大小小找不到”的原则是解答此题的关键.11.【分析】过点D作DE⊥AB,垂足为E,分点E在AB上或AB的延长线上两种情况,分别利用三角函数求出AE、DE的长,利用勾股定理求出BE的长,继而可得AB的长,然后利用平行四边形的面积公式进行求解即可.【详解】过点D作DE⊥AB,垂足为E,如图1,点E在AB上,∵∠A=30°,∴DE=ADsin30°=AE=ADcos30°=6,在Rt△DBE中,2=,∴AB=AE+BE=8,∴平行四边形ABCD的面积为8⨯=如图2,点E在AB的延长线上,∵∠A=30°,∴DE=ADsin30°=AE=ADcos30°=6,在Rt△DBE中,2=,∴AB=AE-BE=4,∴平行四边形ABCD的面积为4⨯=故答案为【点睛】本题考查了解直角三角形,平行四边形的面积,正确地画出图形是解题的关键.12.2.5【分析】过点P 作PF BC ∥交AC 于点F ,根据题意可证APF 是等边三角形,根据等腰三角形三线合一证明AE FE =,根据全等三角形判定定理可证PFD QCD ≌△△,DF DC =,进而证明12DE AC =,计算求值即可.【详解】解:过点P 作PF BC ∥交AC 于点F,∵PF BC ∥,ABC 是等边三角形,∴60,60APF B A ︒︒∠=∠=∠=,∴APF 是等边三角形,∴PF PA =,∵PE AC ⊥,∴AE FE =;∵PA CQ =,∴PF CQ =,∵PF BC ∥,∴∠=∠PFD QCD ,在FPD △和QCD 中,PDF QDC PFD QCD PF QC ∠=∠⎧⎪∠=∠⎨⎪=⎩∴PFD QCD ≌△△,∴DF DC =,∴12DF FC =,12EF AF =,∵,DF EF DE FC AF AC +=+=,∴()11112222DE FC AF FC AF AC =+=+=,∵5AC =,∴115 2.522DE AC ==⨯=,故答案为:2.5【点睛】本题考查了平行线性质、等边三角形性质与判定、全等三角形判定与性质,掌握全等三角形判定定理是解题关键.13【分析】连接AC ,根据正方形的性质可得A 、E 、C 三点共线,连接FG 交AC 于点M ,由正方形的性质求和勾股定理可求得EC 和FG ,AC 的长度,从而求得AE ,因为的中点,可得PE 和AP ,再由正方形的性质可得GM 和EM ,FG ,在Rt △PGM 中,求解即可.【详解】解,如下图,连接AC ,连接FG 与AC 交于点M∵四边形ABCD 和四边形EFCG 是正方形,且点F 、G 分别在边,BC CD 上∴A 、E 、C 三点共线,90,90ABC EFC ∠=∠= ,EC FG ⊥,EC FG=在Rt ABC 中,90,3ABC AB BC ∠=== 由勾股定理得:222223318AC AB BC =+=+=∵AC >0∴AC =在Rt EFC 中,90,1EFC EF FC ∠=== 由勾股定理得:22222112EC EF FC =+=+=∵EC >0∴EC =∴AE AC EC =-=又∵P 是AE 的中点,M 是EC 的中点∴12PM AC ==又∵1122GM FG EC ==在Rt PGM 中,由勾股定理得:222PG PM GM =+即:22222PG ⎛⎛=+ ⎝⎭⎝⎭=5∵0PG >∴PG =【点睛】本题考查正方形的性质,勾股定理解三角形等知识点,牢记性质和定理内容,并结合图形灵活应用是解题关键.14.乙车速度为60千米/时【分析】设甲车速度为x 千米/时,则乙车的速度是34x 千米/时,根据“乙车比甲车晚到90分钟”列出方程并解答.【详解】解:设甲车速度为x 千米/时,则乙车的速度是34x 千米/时,依题意得:360903603604x x +=,解得:80x =,经检验:80x =是原方程的解,∴3604x =,答:乙车速度为60千米/时.【点睛】本题考查分式方程解实际应用题,分析题意,找到合适的数量关系是解决问题的关键.15.(1)CE BF =,CE BF ⊥;(2)成立,证明见解析;(3【分析】(1)证明△BEC ≌△DBF (SAS ),由全等三角形的性质得出CE=BF ,∠BCE=∠DFB ,则可得到结论;(2)延长FD 交BC 于点G ,证明△CBE ≌△△FDB (SAS ),由全等三角形的性质得出CE=BF ,∠ECB=∠BFG ,则可得出结论;(3)分两种情况画出图形,由勾股定理可求出答案;【详解】(1)CE BF =,CE BF ⊥;如图,设CE与BF相交于点M,∵△ABC和△BDE均为等腰直角三角形,∠ACB=∠DBE=90°,∴AC=BC,DE=DB,∵四边形CAFD是平行四边形,∴CA=DF=BC,CA∥DF,∠ACB=∠FDB,∴∠CBE=∠FDB=90°,∴△BEC≌△DBF(SAS),∴CE=BF,∠BCE=∠DFB,∵∠DFB+∠DBF=90°,∴∠BCE+∠DBF==90°,∴∠CMB=90°,⊥.∴CE BF(2)成立证明:如图,延长FD交BC于点G.四边形ACDF是平行四边形,=,∴,AC FD//AC FDDGB ACB∴∠=∠=︒,90∴∠=∠+∠,FDB DGB DBG∴∠=︒+∠,FDB DBG90,∠=︒DBE90∴∠=︒+∠,90CBE DBGFDB CBE ∠=∠,ABC 是等腰直角三角形,AC BC ∴=,又AC DF = ,BC DF ∴=,BD BE = ,CBE FDB ∴V V ≌,CE BF ∴=,ECB BFG ∠=∠,90BFG FBG ∠+∠=︒Q ,90ECB FBG ∴∠+∠=︒,CE BF ∴⊥.(3)如(2)题图,由(2)知∠DGB=90°,BF=CE ,∵∠DBC=30°,BD=2,∴DG=1,,∵AC=3,AC=DF ,∴FG=DF+DG=3+1=4,∴BF =,∴,如图所示,延长CB 交DF 于点M ,∵AC∥DF,AC⊥BC,∴BM⊥DF,∴∠BMF=∠BMD=90°,∵∠MBD=30°,BD=2,∴DM=1,,∵AC=DF=3,∴FM=DF-DM=3-1=2,∴BF==,∴,∴CE【点睛】本题是四边形几何变换综合题,考查了平行四边形的性质,全等三角形的判定和性质,等腰直角三角形的性质,旋转的性质,勾股定理,熟练掌握旋转的性质是解题的关键;16.(1)正方形(2)CF=FE'(3)【分析】(1)由旋转的特征可得到∠E′=∠AEB=90°、∠EBE′=90°、BE′=BE,再由∠BEF =180°﹣∠AEB=90°,可判定四边形BE′FE是正方形;(2)过点D作DG⊥AE于点G,由DA=DE得AG=12AE,再证明△ADG≌△BAE,且由四边形BE′FE是正方形,得到FE′=AG=12CE′,可证得结论;(3)过点D 作DG ⊥AE 于点G ,由旋转及四边形BE ′FE 是正方形可得如下关系:AE =CE ′=FE ′+CF =FE ′+3=BE +3,在Rt △BAE 中根据勾股定理求出BE 、AE 的长,由(1)可知,△ADG ≌△BAE ,得到DG =BE ,AG =BE ,再由勾股定理求出DE 的长.【详解】(1)四边形BE ′FE 是正方形.理由如下:由旋转得,∠E ′=∠AEB =90°,∠EBE ′=90°,∵∠BEF =180°﹣∠AEB =90°,∴四边形BE ′FE 是矩形,由旋转得,BE ′=BE ,∴四边形BE ′FE 是正方形.(2)CF =FE ',证明:如图2,过点D 作DG ⊥AE 于点G ,则∠DGA =∠AEB =90°,∵DA =DE ,∴AG =12AE ,∵四边形ABCD 是正方形,∴DA =AB ,∠DAB =90°,∴∠BAE +∠DAG =90°,∵∠ADG +∠DAG =90°,∴∠ADG =∠BAE ,在△ADG 和△BAE 中ADG BAE AGD AEB AD AB ∠=∠⎧⎪∠=∠⎨⎪=⎩,∴△ADG ≌△BAE (AA S ),∴AG =BE ;∵四边形BE ′FE 是正方形,∴BE=FE′,∴AG=FE′,由旋转得,AE=CE′,∴12AE=12CE′,∴FE′=12AE=12CE′,∴CF=FE'.(3)如图3,过点D作DG⊥AE于点G,∵BE=FE′,CF=3,∴AE=CE′=FE′+CF=FE′+3=BE+3,∵AE2+BE2=AB2,且AB=15,∴(BE+3)2+BE2=(15)2,解得,BE=9或BE=﹣12(不符合题意,舍去),∴AE=9+3=12,由(2)得,△ADG≌△BAE,∴DG=AE=12,AG=BE=9,∴GE=AE﹣AG=12﹣9=3,∵∠DGE=90°,∴DE=【点睛】此题考查了正方形的性质与判定、旋转的性质、等腰三角形的性质、全等三角形的判定与性质、勾股定理等知识点,解题的关键是正确地作出解题所需要的辅助线,构造全等三角形.。
北师大版2021-2022学年八年级数学下册第二次月考测试题(附答案) (2)

2021-2022学年八年级数学下册第二次月考测试题(附答案)一、选择题(共30分)1.把a2﹣a分解因式,正确的是()A.a(a﹣1)B.a(a+1)C.a(a2﹣1)D.a(1﹣a)2.如图,数轴上所表示的不等式的解集是()A.x≥2B.x>2C.x<2D.x≤23.下列图形中,既是轴对称图形又是中心对称图形的是()A.B.C.D.4.如图,在已知的△ABC中,按以下步骤作图:①分别以B,C为圆心,以大于BC的长为半径作弧,两弧相交于两点M,N;②作直线MN交AB于点D,连接CD,若CD=AC,∠B=25°,则∠ACB的度数为()A.105°B.100°C.95°D.90°5.要使分式有意义,则x的取值范围是()A.x=1B.x≠1C.x=﹣1D.x≠﹣16.如图,在▱ABCD中,将△ADC沿AC折叠后,点D恰好落在DC的延长线上的点E处.若∠B=60°,AB=3,则△ADE的周长为()A.12B.15C.18D.217.若(a+3)x>a+3的解集为x<1,则a必须满足()A.a<0B.a>﹣3C.a<﹣3D.a>38.如图,把一块三角板ABC的直角顶点B放在直线EF上,∠C=30°,AC∥EF,则∠1=()A.30°B.45°C.60°D.75°9.如图,一次函数y1=x+b与一次函数y2=kx+3的图象交于点P(1,2),则关于不等式x+b>kx+3的解集是()A.x>0B.x>1C.x<1D.x<010.如图,在△ABC中,AB=AC,分别以点A、B为圆心,以适当的长为半径作弧,两弧分别交于E,F,作直线EF,D为BC的中点,M为直线EF上任意一点.若BC=4,△ABC面积为10,则BM+MD长度的最小值为()A.B.3C.4D.5二、填空题(共24分)11.分解因式:ab2﹣9a=.12.若一个多边形的每一个内角都是150°,则它是边形.13.如图所示,△DEF是由△ABC通过平移得到的,且点B,E,C,F在同一条直线上,若BF=14,EC=8,则从△ABC到△DEF的平移距离为.14.若分式有意义,则x的取值范围为.15.平行四边形ABCD中,E、F是对角线BD上不同的两点,写出一个能使四边形AECF 一定为平行四边形的条件.(用题目中的已知字母表示)16.如图,∠AOB=120°,点P为∠AOB的平分线上的一个定点,且∠MPN与∠AOB互补,若∠MPN在绕点P旋转的过程中,其两边分别与OA、OB相交于M、N两点,则以下结论:①PM=PN;②OM+ON=OP;③四边形PMON的面积保持不变;④△PMN的周长保持不变.其中说法正确的是(填序号).三、计算题(共18分)17.解方程:.18.解不等式组并把解集在数轴上表示出来.19.先化简:,再选一个你喜欢的a的值代入求值.四、解答题(共48分)20.如图,△ABC三个顶点的坐标分别为A(2,4),B(1,1),C(4,3).(1)请画出△ABC关于原点对称的△A1B1C1;(2)请画出△ABC绕点B逆时针旋转90°后的△A2B2C2,并写出A2的坐标.21.如图,在等边△ABC中,AB=6,D是AC的中点,E是BC延长线上的一点,CE=CD,DF⊥BE,垂足为F.(1)求BD的长;(2)求证:BF=EF.22.如图:在Rt△ABC中,∠A=90°,过B作BH∥AC.(1)按尺规作图要求作BC的垂直平分线,交AC于E,交BH于D,(保留作图痕迹,不写作法),连接BE、CD.(2)求证:四边形BECD是平行四边形.23.为了做好防疫工作,学校准备购进一批消毒液.已知每瓶B型消毒液比A型贵2元,用56元购A型消毒液与72元购B型消毒液的瓶数相同.(1)这两种消毒液的单价各是多少元?(2)学校准备购进这两种消毒液共90瓶,且B型消毒液的数量不少于A型消毒液数量的,请设计出最省钱的购买方案,并求出最少费用.24.如图,在▱ABCD中,对角线AC,BD相交于点O,BD=2AD,点E在线段OC上,且OE=CE.(1)求证:∠OBE=∠ADO;(2)若F,G分别是OD,AB的中点,且BC=10,①求证:△EFG是等腰三角形;②当EF⊥EG时,求▱ABCD的面积.25.如图,在平面直角坐标系xOy中,已知点A(5,1),B(1,1),C(0,5).直线m平行于x轴且经过C,D,E三点.直线l的关系式为y=﹣2x+b.(1)若△ABD是以AB为底的等腰三角形,且直线l过点D,求b的值;(2)若b=9,直线l与▱ABDE的边DE相交时,求点E的横坐标n的取值范围;(3)若点F为▱ABDE的对角线BE与DA的交点,当直线l经过点F时,求点D的横坐标q与b之间的函数关系式.参考答案与试题解析一、选择题(共30分)1.解:a2﹣a=a(a﹣1).故选:A.2.解:∵2处是实心圆点且折线向右,∴不等式的解集是x≥2.故选:A.3.解:A.该图形既不是轴对称图形,又不是中心对称图形,故此选项不合题意;B.该图形既不是轴对称图形,又不是中心对称图形,故此选项不合题意;C.该图形是轴对称图形,不是中心对称图形,故此选项不合题意;D.该图形既是轴对称图形,又是中心对称图形,故此选项符合题意.故选:D.4.解:由题意可得:MN垂直平分BC,则DC=BD,故∠DCB=∠DBC=25°,则∠CDA=25°+25°=50°,∵CD=AC,∴∠A=∠CDA=50°,∴∠ACB=180°﹣50°﹣25°=105°.故选:A.5.解:∵分式有意义,∴x﹣1≠0.解得;x≠1.故选:B.6.解:由折叠可得,∠ACD=∠ACE=90°,∴∠BAC=90°,又∵∠B=60°,∴∠ACB=30°,∴BC=2AB=6,由折叠可得,∠E=∠D=∠B=60°,∴∠DAE=60°,∴△ADE是等边三角形,∴△ADE的周长为6×3=18,故选:C.7.解:∵(a+3)x>a+3的解集为x<1,∴a+3<0,解得:a<﹣3.故选:C.8.解:∵AC∥EF,∠C=30°,∴∠C=∠CBF=30°,∵∠ABC=90°,∴∠1=180°﹣∠ABC﹣∠CBF=180°﹣90°﹣30°=60°,故选:C.9.解:当x>1时,x+b>kx+3,即不等式x+b>kx+3的解集为x>1.故选:B.10.解:由作法得EF垂直平分AB,∴MB=MA,∴BM+MD=MA+MD,连接MA、DA,如图,∵MA+MD≥AD(当且仅当M点在AD上时取等号),∴MA+MD的最小值为AD,∵AB=AC,D点为BC的中点,∴AD⊥BC,∵S△ABC=•BC•AD=10,∴AD==5,∴BM+MD长度的最小值为5.二、填空题(共24分)11.解:原式=a(b2﹣9)=a(b+3)(b﹣3),故答案为:a(b+3)(b﹣3).12.解:360÷30=12,则它是12边形.13.解:∵△DEF是由△ABC通过平移得到,∴BE=CF,∴BE=BF﹣EC,∵BF=14,EC=8,∴BE=14﹣8=3.故答案为:3.14.解:∵分式有意义,∴x2﹣4≠0,∴x≠±2.故答案为:x≠±2.15.解:连接AC交BD于点O,如图:在平行四边形ABCD中,OA=OC,OB=OD,∵AE∥CF,∴∠OAE=∠OCF,∵∠AOE=∠COF,AO=CO,∴△AOE≌COF(ASA),∴OE=OF,∴四边形AECF为平行四边形;故答案为:AE∥CF.16.解:过点P作PE⊥OA,垂足为E,过点P作PF⊥OB,垂足为F,∴∠PEO=90°,∠PFO=90°,∵∠AOB=120°,∴∠EPF=360°﹣∠AOB﹣∠PEO﹣∠PFO=60°,∵∠MPN+∠AOB=180°,∴∠MPN=180°﹣∠AOB=60°,∴∠MPN﹣∠EPN=∠EPF﹣∠EPN,∴∠MPE=∠NPF,∵OP平分∠AOB,PE⊥OA,PF⊥OB,∴PE=PF,∵∠MEP=∠NFP=90°,∴△MEP≌△NFP(ASA),∴PM=PN,ME=NF,故①正确;∵OP=OP,∴Rt△PEO≌Rt△PFO(HL),∴OE=OF,∴OM+ON=OE+ME+OF﹣NF=2OE,∵OP平分∠AOB,∴∠EOP=∠AOB=60°,∴∠EPO=90°﹣∠EOP=30°,∴PO=2OE,∴OM+ON=OP,故②正确;∵△MEP≌△NFP,∴四边形PMON的面积=四边形PEOF的面积,∴四边形PMON的面积保持不变,故③正确;∵PM=PN,∠MPN=60°,∴△PMN是等边三角形,∵MN的长度是变化的,∴△PMN的周长是变化的,故④错误;所以,说法正确的是:①②③,故答案为:①②③.三、计算题(共18分)17.解:方程两边同乘以(x+1)(x﹣1)得(x+1)2﹣6=(x+1)(x﹣1)(2分)整理,得2x=4x=2(4分)检验,把x=2代入(x+1)(x﹣1)=3≠0.所以,原方程的根是x=2.(5分)18.解:解不等式x+4≤3(x+2),得:x≥﹣1,解不等式3x﹣3<2x,得:x<3,则不等式组的解集为﹣1≤x<3,将不等式的解集表示在数轴上如下:19.解:原式=[﹣]•=•=•=,当a=﹣1时,原式=﹣1.四、解答题(共48分)20.解:(1)如图,△A1B1C1;即为所求;(2)如图,△A2B2C2即为所求,A2的坐标(﹣2,2).21.(1)解:∵△ABC是等边三角形,∴∠BCD=60°,AB=BC=AC=6,又∵AB=6,点D为AC的中点,∴CD=3,BC⊥CD,∴BD===3;(2)证明:∵△ABC是等边三角形,D为AC的中点,∴∠CBD=,又∵CE=CD,∴∠CDE=∠E,又∵∠BCD=60°,∴∠E=,∴∠CBD=∠E,∴BD=DE,又∵DF⊥BC,垂足为F.∴BF=EF.22.(1)解:如图,直线DE为所求;(2)证明:DE交BC于F,如图,∵DE垂直平分BC,∴BF=CF,EB=EC,又∵BH∥AC,∴∠1=∠2,∠3=∠4在△BDF和△CEF中,,∴△BDF≌△CEF(AAS),∴BD=CE,∵BD∥CE,∴四边形BECD是平行四边形.23.解:(1)设A型消毒液的单价是x元,B型消毒液的单价是y元,得,解得.答:A型消毒液的单价是7元;B型消毒液的单价是9元.(2)设购进A型消毒液a瓶,则购进B型消毒液(90﹣a)瓶,费用为w元,依题意可得:w=7a+9(90﹣a)=﹣2a+810,∵k=﹣2<0,∴w随a的增大而减小.∵B型消毒液的数量不少于A型消毒液数量的,∴90﹣a≥a.解得a≤67 ,∴当a=67时,w取得最小值,此时w=﹣2×67+810=676,90﹣a=23.答:最省钱的购买方案是购进A型消毒液67瓶,购进B型消毒液23瓶;最低费用为676元.24.(1)证明:∵四边形ABCD是平行四边形,∴AD∥BC,AD=BC,DO=BO=BD,∴∠ADB=∠DBC,∵BD=2AD,∴AD=DO,∴BC=BO,∵E是CO中点,∴∠OBE=∠OBC,∴∠OBE=∠ADO;(2)①证明:∵BC=BO,∴△BOC是等腰三角形,∵E是CO中点,∴EB⊥CO,∴∠BEA=90°,∵G为AB中点,∴EG=AB,∵四边形ABCD是平行四边形,∴AB=CD,∵E、F分别是OC、OD的中点,∴EF=CD∴EG=EF,∴△EFG是等腰三角形;②解:由①得EF∥AB,∵EF⊥EG,∴EG⊥AB,∵G是AB的中点,∴AE=BE,设CE=x,则AO=CO=2CE=2x,∴BE=AE=3x,在Rt△BEC中,BC=10,∴EC2+BE2=BC2,即x2+(3x)2=102,解得x=,∴AC=,BE=,∴S▱ABCD=2S△ABC=.25.解:(1)∵A(5,1),B(1,1),DA=DB,∴D(3,5),将x=3,y=5代入y=﹣2x+b,∴b=11;(2)∵四边形ABDE为平行四边形,∴DE=AB=4,∵E(n,5),∴D(n﹣4,5),当5=﹣2x+9时,x=2,∵直线y=﹣2x+9与边DE有交点,∴2≤n≤6;(3)∵四边形ABDE为平行四边形,∴DF=F A,∵D(q,5),A(5,1),∴,即,将,y=3代入y=﹣2x+b,∴q=b﹣8.。
陕西省西安市高新区第三初级中学博雅班2023-2024学年八年级下学期第二次月考数学试题(学生版)

2023-2024八下第二次月考数学试题一、选择题:(每小题3分,共24分)1. 下列四个图形中,是中心对称图形的是( )A. B. C. D.2.下列各式:,,,,,,只是分式的有( )A. 2个 B. 3个 C. 4个 D. 5个3. 下列各式从左到右的变形,属于因式分解的是( )A. (x 一4)(x +4)=x 2﹣16B. x 2﹣y 2+2=(x +y )(x ﹣y )+2C. x 2+1=x (x +)D. a 2b +ab 2=ab (a +b )4. 如图,四边形中,对角线、相交于点,下列条件不能判定这个四边形是平行四边形是( )A. ,B. ,C. ,D. ,5. 若关于x 的不等式组有且只有3个整数解,则a 的取值范围是( )A. B. C. D.6. 如图,在平面直角坐标系中,等边三角形的边长为4,点在第二象限内,将沿射线的方向平移后得到,平移后点的横坐标为,则点的坐标为( )的23πa b -22x x y -34a b +31x x +-2m -a m 1xABCD AC BD O AB DC AD BC∥AB DC =AD BC =AO CO =BO DO=AB DC =AD BC ∥35128x x a -⎧⎨-<⎩…02a ≤≤02a ≤<02a <≤02a <<OAB A OAB AO O A B '''△A 'B 'A. B. C. D. 7. 精元电子厂准备生产5400套电子元件,甲车间独立生产一半后,由于要尽快投入市场,乙车间也加入了该电子元件的生产,若乙车间每天生产的电子元件套数是甲车间的1.5倍,结果用30天完成任务,问甲车间每天生产电子元件多少套?在这个问题中设甲车间每天生产电子元件x 套,根据题意可得方程为( )A. B.C. D. 8. 如图,菱形的对角线相交于点O ,点P 为边上一动点(不与点A ,B 重合),于点E ,于点F .若,,则的最小值为( )A B. C. 4 D. 二、填空题:(每小题3分,共15分)9.有意义,则实数x 的取值范围是___________.10. 如图,用正多边形镶嵌地面,则图中α的大小为 ________度..(-()4-(8,-()8,4-2700270030x 1.5x+=2700270030x x 1.5x +=+2700540030x x 1.5x +=+5400270030x x 1.5x +=+ABCD ,AC BD AB PE OA ⊥PF OB ⊥20AC =10BD =EF11. 如图,在中,的平分线交于点,的平分线交于点,若,,则的长是 _____.12. 如图所示,菱形的对角线、相交于点.若,,,垂足为,则的长为______.13. 如图,在矩形中,,,点在上且点为中点,点为边上的一个动点,为的中点,则的最小值为_________.三、解答题:(共12小题,共81分.)14. 因式分解.(1)3ab 2﹣18ab +27a .(2)(a 2+b 2)2﹣4a 2b 2.15. 解下列各题:(1)解不等式组;(2)解方程:.16. 先化简,再求值:,其中.17. 如图,已知中,,,请用尺规在边上作一个点P ,使得.(保留作图痕迹,不写作法)的ABCD Y ABC ∠AD E BCD ∠AD F 5AB =6AD =EF ABCD AC BD O 6AC =8BD =AE BC ⊥E AE ABCD 3AB =10AD =E AD 2DE .=G AE P BC F EP GF EF +()362453132x x x x ⎧+>-⎪⎨-+-≤⎪⎩43122x x x-=--221161369x x x x -⎛⎫-÷ ⎪--+⎝⎭6x =ABC 90ACB ∠=︒30A ∠=︒AC 2PA PC =18. 在平面直角坐标系中,的三个顶点在格点上(每个方格的边长均为1个单位长度).(1)请画出关于轴对称的图形;(2)将绕点逆时针旋转90°,画出旋转后得到的;(3)在轴上找一点,使的值最小(不写作法,保留作图痕迹).19. 如图,平行四边形,E 、F 两点在对角线上,且,连接.求证:四边形是平行四边形.20. 证明:直角三角形斜边的中线等于斜边的一半.21. 如图,在四边形中,,对角线交于点平分角,过点作交的延长线于点,连接.(1)求证:四边形是菱形;(2)若,求的长.ABC ABC x 111A B C △ABC O 222A B C △x P PA PB +ABCD BD BE DF =AE EC CF FA ,,,AECF ABCD AB DC AB AD =∥,AC BD ,,O AC BAD ∠C CE AB ⊥AB E OEABCD 4AB BD ==OE22. 已知,如图,和都是等腰直角三角形,,为边上一点.(1)求证:≌;(2)求证:.23. 樱桃刚一上市,某水果店的老板就用6000元购进了一批樱桃,上市后销售的非常好,老板又用14000元购进了第二批樱桃,所购箱数是第一批的2倍,但进价比第一批每箱多了5元.(1)该超市两批共购进樱桃多少箱?(2)由于储存不当,第二批购进的樱桃中有腐坏,不能售卖.该老板将两批樱桃按同一价格全部销售完毕后获利不低于8000元,则每箱樱桃的售价至少是多少元?24. 如图,在平面直角坐标系中,直线:与轴交于点,直线与直线、轴分别交于点、点.(1)求直线的解析式;(2)若点和点分别是直线和轴上动点,是否存在点、,使得以点、、、为顶点、为一边的四边形是平行四边形?若存在,请求出点的坐标;若不存在,请说明理由.25. 问题提出:(1)如图1,在中,,点D 、E 分别是、的中点,则的长为_________;问题探究:(2)如图2,在中,,点Q 在上,,点P 在上,,连接,E 、F 分别为、的中点,求的长度?问题解决:的ACB △ECD 90ACB ECD ∠=∠=︒D AB ACE BCD 2222CD AD DB =+10%1l 112y x =+x B 2l 1l x 31,2A ⎛⎫ ⎪⎝⎭()4,0C 2l D E 2l y D E A B D E AB D ABC 4BC =AB AC DE ABC =60B ∠︒BC 12CQ =AB 4AP =PQ AC PQ EF(3)西安高新区为了进一步提升周边居民居住环境,拟在一个长方形的草坪内对角线右侧修建一个三角形池塘.如图3,,,A 为草坪入口,B 为草坪出口,在人行道的中点E 处有一个凉亭,在池塘N 处是一个观景台.游客从凉亭到出口的距离与从凉亭到观景台的距离相等吗?为什么?的ABCD AC CMN 26MCN ∠=︒90MNC ∠=︒AM。
2023~2024学年度第二学期第二次月考试题八年级物理(下)

2023~2024学年度第二学期第二次月考试题八年级物理(下)一、单选题(共40 分)1. 下列物体重约为1N的是()A.一支铅笔B.一根香蕉C.一瓶矿泉水D.一桶食用油2. 在下列说法中,正确的是()A.船桨是费力杠杆B.物体运动速度越大其惯性越大C.运输机起落架装有宽大的轮子是为了减小对地面的压力D.运动的物体不受力时,运动的速度会减小,最终会停下来3. 目前,我国“天宫”空间站已实现航天员长期驻留,航天员在空间站中可以实施的是()A.用托盘天平测物体质量B.用哑铃锻炼手臂肌肉C.用弹簧测力计测量物体重力D.用弹簧拉力器健身4. 如图所示,一个装有水的平底密闭矿泉水瓶,先正立放置在水平桌面上,再倒立放置。
两次放置时,瓶对桌面的压力分别为F甲和F乙,瓶对桌面的压强分别为p甲和p乙,则()A.F甲>F乙B.p甲>p乙C.F甲<F乙D.p甲<p乙5. 如图所示,O为轻质杠杆AB的支点,B点挂一重物G,若在B点施加F1、或在A点分别施加F2、F3、F4四个力后,杠杆均保持水平位置平衡,则这四个力中最小的力是()A.F1B.F2C.F3D.F46. 把体积相同、质量不同的三个小球A、B、C放入同种液体中,静止后的位置如图所示,它们所受的浮力分别为F A、F B、F C,则这三力大小关系正确的是()A.F A>F B>F CB.F A=F B=F CC.F A<F B<F CD.F A<F B=F C7. 关于下面四幅图的说法中错误的是()A.图甲所示托里拆利实验中,将竖直玻璃管倾斜,水银柱的高度不变B.图乙所示排水管U形“反水弯”是一个连通器C.图丙所示在B管吹气,A管中水而上升,是因为流体中流速越大的位置压强越大D.图丁所示把这自制气压计从山下移到山顶,细管内的水柱上升8. 下列说法中正确的是()A.做功越多的机械,功率一定越大B.功率越大的机械,机械效率越大C.功率越大的机械,所用时间越少D.功率越大的机械,做功一定越快9. 如图所示,小黄家里悬挂着的吊灯处于静止状态,以下说法正确的是()A.天花板对绳子的拉力与绳子对灯的拉力是一对平衡力B.绳子对灯的拉力与灯受到的重力是一对平衡力C.天花板对绳子的拉力与灯受到的重力是一对平衡力D.吊灯对绳子的拉力与绳子对吊灯的拉力是一对平衡力10. 如图所示,细线上端固定,下端拉着小球在竖直平面内摆动,A、B是球摆动过程中的最高点,C是最低点,当小球到达C点时,所受的力全部消失,则小球将()A.一定处于静止状态B.一定做匀速直线运动C.可能处于静止状态可能做匀速直线运动D.可能加速运动二、填空题(共32 分)11. 如图甲所示,工人师傅实际上是因陋就简制成了一个简单的工具,这是利用了重力的方向总是___________的知识;如图乙所示,在A、B、C三点用扳手拧螺母,更省力的是___________点,这说明力的作用效果跟它的___________有关。
学年人教版八年级(下)第二次月考历史试卷

学年内蒙古鄂尔多斯市东胜二中八年级(下)第二次月考历史试卷一、单项选择题(每题2分,共60分)1.中华民族在近百年艰苦卓绝的伟大复兴历程中,关键是“中国新生”和“伟大转折”,实现了国家的独立与富强.“中国新生”和“伟大转折”分别是指()A.中国共产党成立、抗战胜利B.新中国诞生、十一届三中全会C.抗战胜利、新中国诞生D.中国共产党成立、新中国诞生2.中共十一届三中全会是我国历史上的伟大转折,下列叙述正确的是()①确立了解放思想、实事求是的思想路线②把党和国家的工作重心转移到经济建设上来③形成了以邓小平为核心的党中央领导集体④决定设立经济特区。
A.①②③B.②③④C.①③④D.①②③④3.发展民主,健全法制,是社会主义制度的内在要求。
下列选项中,和表格对应正确的是()宪法或宪法性文件主要内容历史评价①规定了新中国在政治、经济、文化、民族和外交方面的基本政策具有临时宪法性质1954年宪法确立人民代表大会制度为根本政治制度②③规定了我国的根本制度和根本任务,确定了四项基本原则和改革开放的基本方针推进了新时期民主法制建设A.①《共同纲领》②我国第一部新民主主义类型的宪法③1978年宪法B.①《共同纲领》②我国第一部社会主义类型的宪法③l982年宪法C.①《土地改革法》②我国第一部新民主主义类型的宪法③1978年宪法D.①《土地改革法》②我国第一部社会主义类型的宪法③1982年宪法4.在中国国家博物馆里,收藏着藏品号为GB54563的一纸契约,它是某地的农民“包产到户”的“地下协议”。
它被作为中国当代史的珍贵文物收藏。
“某地”指的是()A.广东深圳B.安徽凤阳C.浙江温州D.天津大邱庄5.新中国成立后,农业生产关系四次调整的先后顺序是()①土地改革②人民公社化运动③三大改造④家庭联产承包责任制.A.①②③④B.④③①②C.①③②④D.③④②①6.20世纪90年代中期开始,江苏省组建了沙钢集团、春兰集团、徐州工程集团等大型企业集团,实行股份制改造,加快建立现代企业制度。
新目标八年级下学期英语第二次月考试题及答案

八年级下学期英语第二次月考试题一.单项选择(20分)()1. They ______money to build a new school for the faraway village.A.collectedB.tookC.spent D raised()2. He said he _____ doing some shopping.A.would likeB.likedC.wanted D felt()3. ----When did you get the gift? ---- _____ my _____ birthday.A. On, sixthB. In, sixthC. On, sixD. In, six()4. We had to stop to have a rest,____ we were very tired.A.whileB.whenC.whether D because()5. -_____you _____ to New York?-No,but I will go there next year.A.Have,goneB.Do,goC.Will,go D Have,been()6. People are _____ in ______ places.A.interested, interestedB.interesting, interestingC.interested, interestingD.interesting, interested()7. The student_____ No.1 Middle School won the match.A.fromB.inC.atD.of()8. Wen Li has_____ kites for two years.A.been makeB.makingC.been makingD.been made()9. Li Chen _____football an hour ago.A.has been playingB.has playedC.playsD.played()10.-____you_____the film yet? -Yes. I____it last SaturdayA.Will,see;sawB.Did,see;sawC.Have,seen;have seenD.Have,seen;saw()11.“Harry Potter”is a very nice film. I____ it twice.A.will seeB.have seenC.sawD.see()12. ---Do you mind if I open the window? ------__________.A. No, not at allB. Sorry, I’ll do it right awayC. Yes, pleaseD. I’ll be glad to()13. Why not _____ help when you were in trouble?A. you ask forB. ask forC. asking forD. asked for()14. He got really ____ while hearing the bad news.A. angrilyB. angryC. happyD. happily()15. Dogs are too difficult to _______.A. take careB. look forC. give awayD. take care of()16. I have an _____ grandmother.A. 80 year oldB. 80-year-oldC. 80 years oldD. 80-years-old ()17.Tomorrow is Sunday. How about ______ to visit your grandmother?A. goB. goingC. to goD. gone()18. What’s the best gift you ____ ever ____?A. have; receiveB. did; receiveC. have; receivedD. /; receive()19. One of the ____ polite ways ask someone is “Would you mind…?”A .much B. more C. many D. most()20.I go back until the storeA. won't; closesB. will; closesC. don't; will closeD. would; closed二.完形填空(20分)Ted sat next to me when we were in elementary school. He had 1 problems in communicating(交流)with people. One always had to 2 what he was saying. Besides, most of my classmates did not like to be with him 3 his hands and shirts were always 4 .I tried to let him know the 5 of being clean by telling him several times a day to wash his hands. But he didn't want to 6One day, our teacher Miss White walked up to Ted. Without saying 7 ,she took Ted to the washroom. Slowly,Miss White washed his hands and told him that he should 8 himself clean. She did that every day for one month. Finally,Ted understood.Miss White's love has given me a good 9 to follow when I'm doing my job.I always remember to teach my students by showing them the right ways to do things. And most important of all,I 10 remember to give them more time to learn and to grow up.()1. A. great B. important C. necessary D. serious()2. A. repeat B. know C. guess D. so()3. A. if B. because C. why D. so()4. A. old B. dirty C. new D. clean()5. A. importance B. why C. time D. place()6. A. listen B. think C. understand D. hear()7. A. everything B. nothing C. something D. anything ()8. A. get B. have C. keep D. make()9. A. lesson B. example C. advice D. book()10. A. often B. usually C. always D. sometime三.阅读理解(20分)AOne of my friends Fred did very 1ittle work when he was a student. He spent more time drinking in bars than working in the library. Once, we had to take an important exam. The exam had a hundred questions. To each question, we had to write "Right" or "Wrong". The night before the exam, Fred was watching TV and drinking. He usua1ly worried a lot the night before the exam. But on that night he looked quite relaxed. He told me what he would do." It's very easy," he said to me, "There are a hundred questions and I have to get fifty right answers to pass the exam. I'll bring a coin with me and throw it to decide answers. I' m sure I'll get half the questions right in this way." During the exam, Fred sat down and really threw the coin for half an hour when he was writing down his answers. Then he 1eft half anhour before the others. The next day he saw the teacher on the playground. "Good morning, Mr. Wu," he said, "Have you checked the papers? Have I passed?" The teacher 1ooked at him and smiled, "Ah, it's you, Fred. One moment, please." Then he put his hand into his pocket and took out a coin. He threw it into the air, caught it in his hand and looked at it , "I'm very sorry, Fred. You failed."( )1. Fred usually worried a lot before the exam _______________.A. because he did little work in the bars.B. because he did little work on his booksC. he was afraid of the examD. he didn't like taking the exam.( )2. ____________________,the night before the important exam.A. Fred was busy working on his lessonsB. Both Fred and the writer were preparing the lessonsC. Fred worried about the examD. Fred was watching TV and drinking.( ) 3. On that night before the important the exam, Fred was very quiet because _______ .A. he knew the answerB. the exam would be very easyC. the teacher would give him good gradesD. he would choose the answers by chance( ) 4. Which sentence is true?A. The coin didn't bring good luck to Fred.B. The coin brought Fred good luck.C. Fred was a very good student.D. Fred was a very clever student.( )5. Which sentence is wrong?A. The teacher didn't know what Fred did in the examB. Mr. Wu didn't let Fred pass the examC. Mr. Wu was glad that Fred was very clever.D. The next day the teacher looked at Fred and smiled.BOne day Mrs Wilson went shopping with Tracy and Ben. They went to the supermarket in the new shopping centre."Why do you buy things here?" Tracy wanted to know. “Because they are cheaper here than at the corner store near our home.” Mrs Wilson said,“Help me check the prices, please.”The Wilsons were not rich and Mrs Wilson was always careful with her money. She looked carefully at the prices of things. She bought lots of things in the supermarket. When they got home,the children said,"We don't think you saved money by going to the supermarket.”“Of course I did.” Mrs Wilson said. “Everything was cheaper there.”"We know,"the children said,"but we came home by taxi because we had too much to carry. The taxi fare was more than the money you saved!”Mrs Wilson added something up. Her children were right."Well done,”she said. "Next time we'll do the shopping nearby.”()1 .The things at the corner store were_than those in the supermarket.A. cheaperB. niceC. more expensiveD. better()2. Mrs Wilson in the end.A. spent more moneyB. paid less moneyC. lost some moneyD. saved a little money()3. From the passage we know the children were_.A. happyB. cleverC. tiredD. lazy()4. Mrs Wilson will next time.A. never call a taxiB. go on buying things in the supermarketC. buy things near her homeD. not go shopping with her children()5. The best title for the passage isA. Cutting priceB. Corner storeC. SupermarketD. Shopping八年级下册第二次月考答案一.1-5 DBADD 6-10 CACDD11-15 BABBD16-20 BBCD A二.1-5 DABBA 6-10 ADCBC三.1-5 BDDAC 6-10 CABCD。
人教版八年级下册英语第二次月考复习考试试题(Unit1-Unit4)(有答案)

初二英语第二次网上测试试题一、选择题。
(每小题1.5分,共60分)( )1.Dogs ________ run through soccer games at the park.It's dangerous.A. shouldB. shouldn'tC. needD. needn't( )2.My m other found it hard ________ the house.A. cleanB. to cleanC. cleaningD. cleaned( )3.He didn't use to ________ soccer, but now he likes ________ it.A. playing, playingB. play, playingC. playing, to playD. plays, to play( )4.When times are difficult,tell ________ that pain is part of growing.A. youB. yourselfC. yourD. yours( )5.--- Dear, you need to ______ by next week, to go to university at home or to go abroad. You are going on eighteen.--- OK, Mum. I am considering it.A. make an appointmentB. make a suggestionC. make a decision( )6.Tina was too sleepy. She fell asleep _____she was reading a book at the table.A. thenB. untilC. ifD. while( )7.We ________ be more careful,or we will make the same mistake in the experiment.A. mightB. canC. mayD. should( )8 ----Your body temperature is 39。
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八年级物理下册第二次月考试题一、选择题(每题2分,共60分)1.下列选项中,一定具有动能的是()A.汽车 B.飞机 C.巨浪 D.小鸟2.某同学不小心扭伤了脚,你背他去医务室检查,在下列过程中你对他做了功的过程是( )A.把他由地上背到你身上时 B.背着他站着不动时C.背着他在水平路面上行走时 D.背到医务室门前拐弯时3.两台机器正常工作时,功率大的机器一定比功率小的机器( )A.做功多 B.做功少 C.做功快 D.做功慢4.“跳远”是一项常见的体育运动。
跳远运动员在比赛中都是先助跑一段距离后才起跳,这样做()A.增大了跳远运动员的惯性 B.减小了跳远运动员的惯性C.增大了跳远运动员的动能 D.减小了跳远运动员的动能5.下列事例中,能说明“分子在不停地运动”的是()A.发生沙尘暴,沙尘漫天做无规则地运动B.扫地时,阳光下看到微小尘埃不停地运动C.炒菜加点盐后,菜就有了咸味D.将泥沙投入水中搅动,水变浑浊了6.下列关于内能的说法中正确的是()A.晒太阳使身体变暖,是通过做功改变内能的B.热量总是由内能大的物体传递给内能小的物体C.一块0℃的冰融化成0℃的水,内能增加D.物体的内能减少,一定是物体对外做功7.下面事例中,通过热传递方式改变物体内能的是()A.双手相互摩擦,手会变暖和 B.用热水袋焐手,手会变暖和C.反复弯折铁丝,弯折处变热 D.水沸腾后,壶盖被水蒸气顶起8.关于温度、内能、热量三者之间的关系,下列说法正确的是()A.温度高的物体,内能一定大 B.物体温度升高,一定吸收了热量C .物体吸收了热量,温度一定升高D .物体温度升高,内能一定增加9.已知铜的比热容是铅的比热容的3倍,质量相等的铜块和铅块,吸收相同的热量后互相接触.则下列说法中正确的是 ( )A.铜块一定向铅块传热B.铅块不可能向铜块传热C.铜块可能会向铅块传热D.铅块和铜块之间一定有热传递10、甲、乙两机器,甲的机械效率是75%,乙的机械效率是60%,则下列说法中正确的是( )A .甲机器的功率大B .使用甲机器较省力C .甲机器的额外功占总功的百分比较小D .在相同时间内,甲机器做功较多11.起重机匀速提升重为2×104牛顿的工件,提升了100米,又沿水平方向移动了5米,起重机在这个过程中钢丝绳的拉力所做的功是:( )A.3×105焦耳B.105焦耳C.2×106焦耳D.0焦耳12.(2009•达州)如图所示的杠杆是平衡的.若如图乙所示,在支点两侧的物体下方分别加挂一个等重的物体,杠杆( )A .仍能平衡B .不能平衡,A 端上升C .不能平衡,B 端上升D .无法判断13.(2009•南充)如图所示,一根杠杆可绕O 点转动,B 处挂着一重物G ,如果在A 点施加一个如图所示的动力F 使杠杆在水平方向上平衡,则该杠杆为( )A .费力杠杆B .省力杠杆C .等臂杠杆D .以上三种情况都有可能14.(2010•毕节地区)在如图所示的各种情况中,用同样大小的力将重物匀速提升,若不计摩擦和滑轮重,物重最大的是( )15.如图所示,杠杆AOB用细线悬挂起来,当A端挂重G A的物体,B端挂重G B的物体时,杠杆处于平衡状态,此时OA恰好处于水平位置,AO=BO,杠杆重不计,则()A.G A=G B B.G A<G BC.G A>G B D.无法判定16.小明同学用一个距离手3m高处的定滑轮拉住重100 N的物体,从滑轮正下方沿水平方向移动4m,如图所示,若不计绳重和摩擦,他至少做功 ( )A.200J B.300JC.400J D.500J17.一木块重30N,在大小为10N的水平拉力作用下,10s内沿水平地面匀速前进5m,则重力对木块做的功是( )A.0J B.150J C.50J D.200J18.在空中沿水平方向匀速飞行的一架飞机,正在向灾区空头物资,空投过程中,飞机的动能和势能的变化情况是()A.动能和重力势能都增大B.动能和势能都减小C.动能减小,重力势能增大D.动能不变,重力势能不变19.人造卫星沿椭圆轨道绕地球运行,图3所示为卫星从远地点向近地点运动的过程。
针对该过程,以下说法正确的是()A.动能逐渐增大,机械能增大B.势能逐渐减小,机械能减小C.动能逐渐增大,势能逐渐减小,机械能不变D.动能逐渐增大,势能逐渐减小,机械能减小图320.人体的运动系统相当复杂,但最基本的运动形式是,骨骼在肌肉提供的动力作用下绕关节转动。
如图7所示是手端起茶杯的情景,其前臂骨骼相当于杠杆,肱二头肌收缩提供动力。
由图7可以看出,这是一个()A.费力、省距离的杠杆B.省力、费距离的杠杆C.费力、也费距离的杠杆 D.省力、也省距离的杠杆21.如图7所示,在水平拉力F的作用下,物体A匀速向右滑动时,弹簧秤示数为10N,不计滑轮重及滑轮与绳之间摩擦,则水平拉力F和物体A与水平面之间的摩擦力f的大小分别是()A.F=20N,f=20N B.F=10N,f=20NC.F=20N,f=10N D.F=10N,f=10N22.如图所示,用相同的滑轮不同的绕法提起相同的重物,摩擦力可以忽略不计,在物体匀速上升的过程中()A.甲图省力,机械效率甲图大B.甲图省力,机械效率一样大C.乙图省力,机械效率乙图大D.乙图省力,机械效率一样大23.下列叙述中能够提高机械效率的是()A.增加有用功 B.减小机械间的摩擦C.减小总功 D.使用最省力的机械24.将一铁块投入到装有水的烧杯中,它们之间没有发生热传递,这是因为()A.它们具有相同的热量 B.它们具有相同的内能C.它们具有相同的温度 D.它们具有相同的质量25.质量相等的一杯冷水和一杯热水升高相同的温度,则它们吸收的热量()A.初温不知,无法判断 B.一样多C.热水吸收的热量多 D.冷水吸收的热量多26.某同学在劳技课上,用切割机把一个铜块切成了两半,则其中的一半铜块()A.密度、比热容均减小一半 B.密度、比热容均不变C.密度减小一半,比热容不变 D.密度不变,比热容减小一半27.质量相等的两块金属同时从沸水中取出来放在冰上,能使冰熔化得较多的那块金属具有()A.较大的体积 B.较大的密度C.较大的比热容 D.较小的比热容28、在日常生活中,用100N的拉力不能提起重150N的物体的简单机械是 ( )A.杠杆B.斜面C.一个定滑轮D.一个动滑轮29用“分子的观点”解释下列现象,不正确的是()A.水结成冰一一分子发生变化 B.气体易被压缩一一分子间隔大C水加糖变甜一一分子不停地运动 D.铁块很难压缩一一分子间存在斥力30、两台机械所做的总功之比是之2∶1,它们的机械效率之比是3∶4,则它们所做的有用功之比为:()A.2∶1B.3∶4C.8∶3D.3∶2二、填空题(每空1分,共10分)31.某人利用滑轮组把重200 N的物体提升3 m,如果滑轮组的机械效率是60%,则人做的有用功是______ J,额外功是______J,总功是______J.32、如图所示,物体重G=500N,滑轮重10N,当物体G匀速上升时,则挂钩B承受拉力为_________ N,拉力F为_________ N,若绳子自由端向上拉动2m,则物体向上移动_________ m.(不计摩擦、不计滑轮重)33.物体内能的改变有两种方法,下列现象中内能的改变是哪一种方法。
(1)用打气筒给自行车打气时气筒会发热,是______使气体内能改变。
(2)冰块在阳光下熔化成水是_______使冰块的内能改变。
34.小明沿水平方向用力推静止在水平地面上的桌子,但没有推动,此时他对桌子的推力桌子所受到的阻力(填“大于”、“小于”或“等于”),此过程中小明 (填“有”或“没有”)做功。
三、实验作图题(35题每空2分,36题每个做图5分)35.我们都做过“探究杠杆平衡条件”的实验.(1)实验前没有挂钩码时,若杠杆左端下倾,则应将右端的平衡螺母向_________ (选填“左”或“右”)调节,使杠杆在水平位置平衡,实验前使杠杆水平平衡的目的是_________ .(2)实验中,用图所示的方式悬挂钩码,杠杆也能水平平衡(杠杆上每格等距),但老师却往往提醒大家不要采用这种方式.这主要是因为该种方式(_________ )A.一个人无法独立操作 C.力臂与杠杆不重合B.需要使用太多的钩码 D.力和力臂数目过多(3)图中,不改变支点O右侧所挂的两个钩码及其位置,保持左侧第_________ 格的钩码不动,将左侧另外两个钩码改挂到它的下方,杠杆仍可以水平平衡.(4)、杠杆的平衡条件是:36、作图(1) 下面左图是一杠杆图,试画出作用在杠杆A端使杠杆在图示位置平衡的最小动力的示意图并画出该力的力臂。
(2)下面右图是未装配好的滑轮组,请在图中画出滑轮组的绕绳方法,要求使用该滑轮组提升重物时最省力。
四、计算题39.(4分)在小型建筑工地,常用简易的起重设备竖直吊运建筑材料,其工作原理相当于如图所示的滑轮组.某次将总重G为4 000N的砖块匀速吊运到高为10m的楼上,用时40s,卷扬机提供的拉力F为2500N.求在此过程中:(1)绳子自由端移动的速度(2)有用功.(3)拉力F做的功.(4)滑轮组的机械效率.(5)拉力做功的功率.。