第一篇：八年级英语下册第八单元练习题1大全
八年级下册第八单元练习题
一．单项选择。
()1.What should I get my mom _______ her birthday?
A.forB.onC.atD.in
()2.Why don't you ______ a camera? That’s too cheap.A.gotB.getC.getsD.getting
()3.What’s the best gift John ____ ever received?
A.haveB.hasC.hadD.having
()4.Why ______him clean the classroom?
A.not you helpB.don’t helpC.not helpD.not helping
()5.Mrs Green is a ___________ woman.A.30 yearsB.30 yearC.30-year-old D.30-years-old
()6.Goldfish are easy _______________.A.look after B take care C to looking after D to take care of
()7.The girl was too young _________ to school.A.not to goB to goC for goD to going
()8.Peter spends lots of time _________books.A.looking atB onreadC in seeingD reading
()9.Please remember _____off the light before you leave.A.turnB turningC to turnD to get
()10.Every day I have enough time _____ my dog.A play withB playing andC to play withD to play
二．用所给词的正确形式填空。
1．I went shopping instead of________TV at home.(watch)
2．There are some_____ in the house.(mouse)
3．That machine is making a ______(noisy)
4．We _________ any classes next week.(not have)
5.He wants to buy a______car.(person)
6．That book is _______enough.(interest)
三．根据提示，把下列的句子翻译成英语。
1.鹦鹉是最不寻常的动物。
______ are ___________________ pets.2.这些天来最流行的宠物是大肚猪。
The ______ kind of pet _____________ is the ______ pig.3.Tom养了一只叫做Connie的乌龟.Tom has a _____________ Connie.4.这些书将会被赠送给孩子们。
These books will _________________ to children.5.电影太无聊了，演了一半我就睡着了。
初中英语
八年级英语 1
The movie was too broing.I ___________ half way through it.四． 把下列各句重新排列，使之成为一段通顺的对话
A.Mm.I have no idea...OK, some flowers!Give her some flowers with best wishes.I think they’ re the best gifts for her!
B.The day after tomorrow is my mother’ s birthday.What should I get her?
C.Yeah!Good idea!I will help her finish housework and then give her the beautiful flowers!
D.Does she like little animals? Why don’ t you get her a pet cat?
E.No way.It’ s too expensive and I haven’ t enough money to buy it.F.Great!I think your mother will happy to receive your gift.G.No, she doesn’t like them at all.H.Yes, I’d love to.I.What about a camera? I think it’ s a nice gift for your mother.J.Thank you!Will you go and buy the flowers with me?
1.______2.______3.______4.______5.______
6.______7.______8.______9.______10.______
五．阅读理解。
(一)In almost every big university in the United States football is a favorite sport.American football is not like soccer.Players sometimes kick the ball, but they also throw the ball and run with it.They try to take it to the other end of the field.They have four chances to move the ball ten yards.They can carry it or throw it.If they move it to the end of the field, they receive six points.This is called a touch—down.It is difficult to move the ball.Eleven men on the team try to stop the man who has the ball.If the man does not move the ball ten yards, his team kicks the ball to the other team.Each university wants its team to win.Thousands of people come to watch.They all yell for their favorite team.Young men and women called cheerleaders come on the field to help the people yell more.They dance and jump while they yell.Each team plays ten or eleven games each season.The season begins in September and ends in November.If a team is very good, it may play another game after the season ends.The best teams play again on January 1st, the first day of the New Year.Many people go to see these games and many others watch them on television.()1.In American football players can ___.A．only kick the ball
B．only throw the ball
C．only carry the ball
D．kick, throw and carry the ball
()2.If a team wants to get points, it has to move the ball ___.A.10 yardsB.to the other end
C.40 yardsD.away from its own end
()3.Who are dancing and jumping while they yell?
A．The cheerleaders.B．All those who are watching the game.C．The winners.D．The players of both sides.()4.Most teams play games in ___.A.springB.summer
C.autumnD.winter
()5.When do the best teams play again?
A.At Christmas.B.Before the season ends.C.On New Year’s DayD.On the last day of season
(二)仔细阅读下面的文章，然后选择正确答案
Our eating habits are very important for good health and a strong body.There are times when most of us like eating sweets and ice cream better than meat and rice.Sweets and ice cream are not bad for us if we eat them at the end of a meal.If we eat them before a meal, they may take away our appetite(食欲).It’s important for us to eat our meal at regular(规律)time each day.When we feel worry or excited, we may not want to eat.A long time ago, in England, some judges often decided whether a man was telling truth by giving him some dry bread.If the man could not swallow(吞)the bread, it meant that he wasn’t telling the truth.Though this seems strange and foolish they thought it was good way of finding out truth.A man who is worrying something has difficulty in swallowing anything dry, because he loses his appetite.()1.Good eating habits make us ________.A.strongerB.happier
C.more beautifulD.more polite
()2.It’s good to eat sweets and ice cream ________.A.after a mealB.before a meal
C.when we are happyD.when we want to eat
()3.It’s good for us to have our meal ________ every day.A.earlierB.at the same time
C.at any timeD.at the different time
()4.The judge in old England thought if a man didn’t tell me the truth, he can ________.A.drink milk or teaB.eat a lot of dry bread
C.hardly eat dry breadD.swallow dry bread easily
七．书面表达
明天是妈妈的生日，你和爸爸商量给妈妈买什么做礼物，编一段对话。
以下词汇可供参考。
creative enoughpay forgive awayenough money
第二篇：英语八年级下册第八单元总结
Unit 8 why don’t you get her a scarf ?
1.表示建议的句型
Why don’t you do sth? =why not do sth? 8.what a lucky guy he is!=how lucky the guy is!How about sth?=what about sth? Shall we do sth? Let’s do sth?
Would you like to do sth? 表同意:Good idea.Sounds good.I agree with you.Why not? I think so.表否定： I disagree with you.Bad idea.I don’t think so.2.buy sth for sb=buy sb sth=get sb sth 3.adj.+enoughenough+n.4.give sb sth =give sth to sb 5.not creative enough 不够创新 6.gift giving
7.instead of+doing /n./pron.Instead放词尾 9.Receive 收到 是客观上的 Accept 接受 是主观上的 10.learn doing/ to do sth 11.try on 试穿
12.比较级+than +any other+n.任何一个都）
13.One of +the +最高级+n复数 14.Run out of
15.From across china=from all over china 16.Encourage sb to do sth 鼓励某人做某事 17.Take/have an interest in=be interested in 18.Make much/great progress by doing sth通过做某事取得巨大进步
19.rather than而不是,与其……不如……。可作为一个连词词组,用来连接两个并列成分,表示在两者中进行选择,意为“是A而不是B”,“要A不要B”,“宁愿A而不愿B”。后面可以接名词、名词短语、代词、形容词、副词、动词、不定式、动名词等
第三篇：人教版八年级英语下册教案第八单元
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Unit8 Why don’t you get her a scarf?
全国中考信息资源门户网站 www.xiexiebang.com
全国中考信息资源门户网站 www.xiexiebang.com
全国中考信息资源门户网站 www.xiexiebang.com
全国中考信息资源门户网站 www.xiexiebang.com
全国中考信息资源门户网站 www.xiexiebang.com
全国中考信息资源门户网站 www.xiexiebang.com
全国中考信息资源门户网站 www.xiexiebang.com
全国中考信息资源门户网站 www.xiexiebang.com
全国中考信息资源门户网站 www.xiexiebang.com
第四篇：2013年人教版七年级英语下册第八单元练习题pi
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2012年版七年级英语下册Unit 8单元测试
Section A
1.根据句意及首字母提示完成单词
1.2.3.4.5.Can you go to the p_________ office to send a letter for me? Tom is ill in h_________.Let’s go to the r__________ and eat some food.We often buy a lot of things in the s__________ on Sundays.You should put the money in the b_______.2.从括号中选择恰当的介词填空
（between, to, from, on, of）xK b1.Co m
1.The library is across _______ my home.2.Tuesday is ________ Monday and Wednesday.3.Is the hospital next _______ the park or far ________ it?
4.The restaurant is ________ the other side of the street.5.The supermarket is in front ________ the school.3.单项选择
1.Can you swim _______ the river?()
A.nearB.betweenC.fromD.across
2.________ , where is the park?()
A.HiB.HelloC.Excuse meD.Excuse
3.The hotel is ______ the bank.()
A.acrossB.fromC.across formD.next 新 课标第一 网
4.We ______ a big family.()
A.areB.haveC.hasD.there are
5.There isn’t a restaurant ______ here.()
A.inB.nearC.fromD.on
6.----Thank you very much..()
----____________
A.You’re welcome.B.Really?
C.Nice to meet you.D.Thank you,too.7.----Is there a library in your school?()
----___________.A.Yes,it is.B.No,it isn’t.C.Yes,there is.D.No,there aren’t.8.----_______ is the park?()
----It’s on the right of the school.A.WhereB.WhatC.WhyD.How
9._______ any books on the desk?()X|k | B| 1.c|O |m
A.There isB.There areC.Is thereD.Are there
10._________ something wrong with my bike.Can I use yours?()
A.It isB.It wasC.There isD.There was
4.句型转换 对划线部分提问)
________ ________ near the library?
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2.There is a pay phone near the school.(改为一般疑问句)
________ ________ a pay phone near the shool? 对划线部分提问)
____________ the hotel?
4.There is a pen in my pencil case.(改为同义句)
I ________ a pen in my pencil case.5.阅读理解
Johnson likes swimming in a small river near his house.But then his father goes to work in a big city and Johnson goes with his family.Their new house has a garden ,but the garden is very small Johnson is not very happy.“Is there a river near the house ?”he askes his father on the first morning.” No, there isn’t.But there is a big park near here.And there’s a pool in it.“ “We are going there this afternoon.“says his father.Johnson is happy.新|课 | 标|第|一| 网
Johnson and his father go to the park in the afternoon.Johnson wants to walk near the pool.Ut he sees a sign.His father reads it to him: “Warning : This pool is dangerous.365 people fell into it.“Johanson looks into the pool carefully , then he says ,”I can’t see them.()1.There is a _______ near Johnson’s new house.A.small riverB.big parkC.small gardenD.big pool
()2.John isn’t very happy because __________.A.there isn’t a big park
B.there’s a pool
C.his father goes to work in a big city
D.there isn’t a river near the newhouse.()3.There is a _______ near the pool.A.signB.riverC.gardenD.tree
()4.The warning tells people ________ near the pool.A to look into itB.not to swim
C.to be carefulD.not to look into it
()5.Which isn’t right ?
A.There isn’t a small river near Johnson’s house.B.Johnson’s father gets a new job in a big city.C.Johanson is afraid to walk near the pool
D.Johnson goes to the big city with his father.Section B
1.单项填空
1.My sister enjoys________the guitar in the park every morning.A.playB.playsC.playingD.to play2、there is a beautiful garden ________fifthavenue（A．onB．inC．atD．with
3.I want to find a house __________ many trees around it.X k B1.c o m
A.withB.haveC.hasD.there are
4.Go ________this sereet and then turn right..A.FromB.toC.downD.on
5.There______some water in the glass.A.isB.areC.beD.has
6.Alice spends too much time _______computer games.A.playB.playsC.to playD.playing
7.Go straight and turn ______.The bank is ______.A.left;leftB.left;on the leftC.on the leftD.left;to left
8.My father has a habit of jogging _______the Jinchuan River for an hour in the morning,A.betweenB.alongC.overD.through
9.Julia ______a bus to work every day,A.bringsB.hasC.getsD.takes
10.I hope you ______a good time.A.to haveB.haveC.hasD.having
2.用所给单词的适当形式填空
1.The children enjoy _______（play）soccer after class.新 课标第一 网
2.She ______（go）home at five every afternoon.3.I spend much time _______(speak)English every morning,4.I can find the hotel ________(easy).5.You should turn right at the second ______(cross).6.I think money ________(be not)everything.7.I love to watch monkeys _______(climb)trees.8.There _______(be)a pen and two pencils in the box.3.根据汉语意思完成句子
1.沿着第五大街走，然后左转。
Go____Fifth Street,then_____________,2.我家在一条喧闹的大街上。
My house is ______a noisy ________.3.从机场坐出租车，沿着公路走，直到看到一个图书馆在你的右边。
_______________________ from the airport and _______________ the road until you see a library ___________________________
4.沿着这条街走。你能很容易地到达图书馆。
_________________.You can get to the library _______.5.请在第一个十字路口处向右拐。
Please ________________ at the first _________.4.完形填空
Mike is an Englishman.He lives in a __1___ building in the __2___ London.There are eighteen floors in the building and he lives on the fifteenth floor.He__3___ a lift(电梯)to go up and down.He works very hard.He__4___ to work early.Every day he leaves his__5__and walks to the lift.He gets into the lift.It __6___him down to the first floor.He gets out of the lift.Then he walks to __7___bus stop.The bus stop is in front of a station.It is about two hundred meters from ___8___home.Usually, he catches the number 11 bus to work, but sometimes he goes__9___.He works in a factory about ten__10___ from his home.His work starts at half past eight, and finishes at a quarter to five.He gets back home at half past5.X k B1.c o m
（）1.A.tall B.shot C.small D.large
（）2.A.country B.town C.city D.village
（）3.A.makes B.uses C.does D.mends
（）4.A.begins B.wants C.runs D.goes
（）5.A.home B.building C.office D.room
（）6.A.costs B.spends C.takes D.brings
（）7.A.an B.a C.the D./
（）8.A.his B.he C.him D.himself
（）9.A.by plane B.by train C.on foot D.by air
()10.A.meters B.kilometers C.minutes D.hours
Self Check 新|课 | 标|第|一| 网
1.任务型阅读
It was the last day of the winter vacation.Li Xin went to bed early in the evening.He wanted to go to school early the next morning because he couldn‟t wait to see his teachers and classmates.The next morning, Li Xin got up at 6:00.He looked“Wow, how beautiful!” said Li Xin.There were many trees in front of his house.They were really beautiful with the white snow.He went out of his house and was going to school.How did Li Xin go to school? There was much snow on the street.He decided to walk to school.Twenty minutes later,Li Xin got to school.Some teachers and students were cleaning the snow outside the classrooms Li Xin did it,too.He was tired ,but he felt happy on the first dayback to school.1.判断正误 Li Xin went to bed early on the evening of the first school day.()
2.补全句子Li Xin wanted to go to school early because_______________________________
3.What were in front ofLi Xin’shouse.?回答问题_______________________________
4.How did Li Xin go to school? 回 答 问 题 _______________________________
5.将划线句子翻译汉语 ____________________________________。
2.完形填空
This is my bedroom.I can see _1_ pictures on the wall.The light is _2_ the desk.The football is _3_ the chair._4_ is the bed? It's near the table.My father and _5_ bedroom is near my bedroom._6_ flowers and a bed _7_ in their room.Some windows are _8_ the wall.A yellow door is in the wall, _9_.I like my bedroom and they like _10_.1.A.aB.oneC.anD.some（）
2.A.underB.onC.inD.behind（）
3.A.onB.underC.toD.for（）
4.A.WhoB.WhatC.WhichD.Where（）
5.A.sisterB.motherC.mother'sD.sisters（）
6.A.TheB.theC.SomeD.some（）
7.A.isB.areC.isn'tD.am（）X k B1.c o m
8.A.onB.behindC.inD.under（）
9.A.alsoB.thereC.hereD.too（）
10.A.alsoB.theirs'C.themD.their room（）
3.书面表达
假如你叫Mike,你的朋友Larry明天要到你所在的城市，但是你没有时间去机场接他。请给他发一封电子邮件，告诉他怎样从机场到你家。要求包括下面的要点，不少于50词。开头和结尾已给出，不计入总次数。
要点提示：
1.先乘出租车从机场到和平路。
2.沿着和平路走，经过一家超市向右拐。
3.穿过第八大街，当看到一个邮局时，向右拐。能看见一座红色的房子，那就是我的家。X k B1.c o m
Dear Larry,I know you are arriving tomorrow.But I am sorry that …
____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________I hope you have a good trip.Yours,Mike
新课标第一网系列资料
第五篇：2018-2018八年级物理第八单元同步练习题
2018-2018八年级物理第八单元同步练习题
为了能帮助广大学生朋友们提高成绩和思维能力，查字典物理网初中频道特地为大家整理了八年级物理第八单元同步练习题，希望能够切实的帮到大家，同时祝大家学业进步!
一、选择题(共18小题，每小题只有一个符合题意的选项，请将这个选项前的字母代号用2B铅笔在答题卡上填涂。每小题2分，计36分)
1.如图所示为小丽向右推墙的情境，下列分析正确的是
A.她推墙时，墙对她没有作用力
B.她推墙后向左运动，离开墙后继续向左运动，是因为受到墙的推力作用
C.她滑行一段距离后会停下来，是因为受到平衡力的作用
D.她静止在水平地面上时，受到的重力与地面对她的支持力是一对平衡力
2.下列有关力的说法正确的是
A.摩擦力是一种总是阻碍物体运动的力
B.物体所受重力的方向始终竖直向下
C.两个物体只有接触才能产生力的作用
D.物体只有漂在液面上才会受到浮力的作用
3.如图所示，关于力的作用效果的说法中，错误的是
A.鱼线对鱼竿的拉力使钓鱼竿发生形变
B.瓶对海绵的压力使海绵发生形变
C.球拍对乒乓球的作用力改变了乒乓球的运动方向
D.脚用力踢足球时，能使足球飞出去，说明力是维持物体运动的原因 4.下列有关于运动和力的说法中正确的是
A.给正在运动的物体再施加一个力，物体一定比原来运动得更快
B.运动的物体如果不受外力的作用时将会慢慢停下来
C.推出去的铅球继续前进是因为受到了惯性的作用
D.跳伞运动员在空中匀速下降时机械能逐渐减小
5.当悬挂在教室的电灯静止时，下列说法正确的是
A.电灯对电线的拉力与电线对电灯的拉力是一对相互作用力
B.电灯对电线的拉力与电线对电灯的拉力是一对平衡力
C.电灯对电线的拉力与电灯受到的重力是一对平衡力
D.电灯对电线的拉力与电灯受到的重力是一对相互作用力 6.下列现象中，不能用惯性知识解释的是
A.司机开车时需要系安全带 B.运动员跳远时需要助跑
C.骑自行车时为了减速捏紧车闸 D.投出去的铅球离开手后继续向前运动
7.如图所示的实例中，为了减小摩擦是
A.旱冰鞋上的滑轮 B.运动鞋底上的花纹 C.浴室脚垫上的颗粒 D.雪天轮胎上绕的链条
8.5月30日，2014年屈原故里端午文化节开幕式暨传统龙舟赛在秭归隆重举行，使龙舟向前行驶的力的施力物体是
A.船桨 B.龙舟 C.舟上选手的手臂 D.江水
9.下列关于力学现象的解释中正确的是
A.人用力推车，车未动，是因为推力小于摩擦阻力
B.苹果在空中下落得越来越快，是因为力是改变物体运动状态的原因
C.汽车刹车后，速度会逐渐减小，最后会停下来，是因为汽车具有惯性
D.书本静止在课桌上，是因为书本受到的重力与书本对桌面的压力平衡
10.如图所示，小叶观察家中的平底茶杯放在水平桌面时的情形时想：如果将空茶杯正放在桌面上对桌面的压力和压强分别为F1和P1，再将它倒扣在同一桌面上对桌面的压力和压强分别为F2和P2，那么F1与F2和P1与P2间的关系正确的是
A.F1 P1=P2 B.F1=F2 P1 C.F1
11.2014年4月28至29日的两天里，31场龙卷风连日袭击美国中南部6周，龙卷风的实质是高速旋转的气流，它能把地面上的物体或人吸起卷入空中，龙卷风能吸起物体的主要原因是
A.龙卷风增大了空气对物体的浮力 B.龙卷风中心区域的气压远小于外部的气压
C.龙卷风使物体受到的重力减小 D.龙卷风产生了强大的万有引力将物体吸上天空
12.下列有关做功的说法正确的是
A.用水平力推着购物车前进，推车的力做了功
B.把水桶从地面上提起来，提水桶的力没有做功
C.书静止在水平桌面上，书受到的支持力做了功
D.挂钩上的书包静止时，书包受到的拉力做了功
13.下面是日常生活中与压强有关事例的描述，其中正确的是
A.图钉帽面积大是为了增大手指对它的压强
B.水电站的拦河坝设计成上窄下宽是因为液体的压强随着液体深度的增加而增大
C.用吸管吸饮料是利用了嘴的吸力
D.高压锅能很快地煮熟食物是对大气压的利用
14.端午节那天，小明发现煮熟的咸鸭蛋甲漂浮在水面，乙沉在水底，如图所示。若甲的体积比乙小，则下列分析合理的是
A.甲的质量比乙大 B.甲受到的浮力等于甲的重力
C.甲的密度比乙大 D.乙受到的浮力大于重力
15.三位同学准备进行爬楼比赛，看看谁的功率大。比赛前他们展开了如下的讨论：
甲：只有测出各自的体重、爬楼用的时间和爬楼的长度，才能进行比较
乙：在爬楼的时间相同时，只要测出各自的体重、爬楼的高度，就可以进行比较 丙：在爬楼的高度相同时，只要测出各自的体重、爬楼的时间，就可以进行比较
A.甲、乙、丙 B.甲、乙 C.甲、丙 D.乙、丙
16.图所示的工具中属于费力杠杆的一组是
A.①② B.②③ C.②④ D.③④
17.一个滑轮组经改进后提高了机械效率，用它将同一物体匀速提升相同的高度，改进后与改进前相比
A.有用功减少，总功减少 B.有用功增加，总功增加
C.有用功不变，总功不变 D.有用功不变，总功减少
18.如图所示，小华把悬挂的铁锁拉近并紧贴自己的鼻子，稳定后松手，头保持不动，铁锁向前摆去又摆回。下列说法正确的是
A.锁不断地来回摆动，是因为动能不断增加 B.锁向下摆的过程中，重力势能转化为动能
C.锁摆到最低点后会继续上升，是因为受到重力作用
D.锁摆动的过程中，摆回来时有可能会碰到鼻子
二、填空题(共7小题，每小题2分，计14分)
19.如图是天宫一号飞行器运行轨道的示意图;若它沿椭圆轨道绕地运行的过程中机械能守恒，则它从远地点向近地点运行的过程中动能，机械能(均选填增大、减小或不变)
20.小强用10N的水平推力匀速推动放在水平地面的课桌，则课桌受到地面对它的摩擦力大小为 N;某同学将该课桌内的书包拿走后，把课桌沿原路用水平力推回的过程中，课桌受到地面对它的摩擦力。(选填增大、减小或不变)
21.一个竖直悬挂在水中的圆柱体，上表面受到水的压力是5N，下表面受到水的压力是13N，那么这个圆柱体受到水的浮力大小是 N，方向是。
22.某校在对学生开展安全教育实践活动中，利用如图的图片告知学生无论汽车落水还是遇雨被淹，都应立刻开门逃生，越迟疑车门越难推开，因为车辆被淹越深，车门下部O处受到水的压强越。紧急情况下，应挥动逃生锤的B端砸向玻璃窗的边角，破窗逃离，因为B端比A端，更容易砸破玻璃窗。
23.如图所示，A、B是两个上端开口的容器，它们构成的是一个当用一个管子沿B容器口吹气时，B容器中的液面会。(填上升下降或不变)
24.潜水艇能够上浮和下沉是通过改变 来实现的;潜水艇在上浮的过程中，未露出水面之前，所受的浮力将。(选填变大、变小或不变)
25.升降式晾衣架结构如图所示，它们实际上是一组简单机械，由固定在墙壁和天花板上的定滑轮和升降钢索的转动摇把组成，可以省了的是，可以改变力的方向的是。
三、实验与探究(第26小题2分，第27、28小题各4分，第29小题5分，计15分)
26.如图所示，课桌的重心在O点，若在课桌的C电用力F把桌腿B抬离地面，在抬起时另一桌腿A没有滑动，请在图中画出力F相对于A点的力臂L1和课桌重力G的示意图。
27.小伟在探究影响滑动摩擦力大小的因素的实验中，他猜想影响滑动摩擦力的大小因素可能用：①接触面所受的压力大小;②接触面的粗糙程度;③接触面积的大小。接着小伟就通过如图13所示的实验来验证他的猜想：
(1)实验中小伟用弹簧测力计水平匀速直线拉动木块在长木板上滑动，这样做是为了利用 的原理得出拉力等于摩擦力，从而测出木块所受摩擦力的大小。
(2)如果小伟要探究猜想②，他应该选择 两幅图所示的实验步骤来操作，根据图中弹簧测力计的示数可得出结论：在压力和接触面积相同的情况下，滑动摩擦力越大。
(3)小伟要探究猜想③，他将木块切去一半，重复甲的操作过程，如图丁所示。它比较甲和丁的实验结果，得出结论：滑动摩擦力的大小与接触面积的大小有关。那么小伟在实验中存在的问题是。
28.如图为小敏同学探究杠杆平衡条件的实验装置。
(1)试验时，小敏同学先调节平衡螺母，使杠杆在水平位置平衡，是为了，通过多次实验，小敏同学得到了用字母表示的杠杆的平衡条件是。
(2)实验中，在杠杆上的A电挂四个重均为0.5N的钩码，用调好的弹簧测力计竖直向上拉杠杆上的B点，使杠杆水平平衡，如图14所示，则测力计的示数应该是 N;如果将测力计沿图中虚线方向拉，仍使杠杆在水平位置平衡，则测力计的示数将。(填变大、不变或变小)
29.小明同学在探究影响浮力大小的因素时，做了如图所示的实验，请你根据小明的实验探究回答下列问题。(水=1.0103kg/m3)
(1)根据图中所标的实验数据，可知物体浸没在盐水中所受的浮力是 N。
(2)根据图C与图E的实验数据，可得出实验结论是：。
(3)根据ABCD四个图中的实验数据，还可以发现当物体浸入同种液体时，物体所受浮力的大小与 有关，与 无关。
(4)根据有关实验数据，可以计算出盐水的密度为 kg/m3。
四、应用与实践(共3小题，第30小题4分，第31小题5分，第32小题6分，计15分)
30.如图所示为小明做俯卧撑的示意图，若把他的身体看做一个杠杆，O为支点，A为重心，他的体重为550N，求：
(1)地面对手的支持力F的大小是多牛?
(2)当他将双手撑地改为单手撑地后，他对地面的压强将如何变化?并说明理由。
船名中国海监5001
型号船长88m型宽12m型深5.6m
满载排水量1500t
巡航速度36km/h 31.2013年6月1日，由武汉造船厂制造的中国海监5001在江苏南通交付使用，它是目前我国最先进的海洋公务执法船。其部分技术参数如下表(海水密度海水=1.0103kg/m3)。求：
(1)海监船由长江驶入大海执行任务时，船体会 一些。(填上浮或下沉)
(2)海监船在某海域巡航时，船底在海水中的深度达到3.0m，求船底受到海水的压强是多少帕?
(3)海监船满载时受到的浮力是多少牛?
32.2014年2月25日宜昌BRT快速公交项目工程建设正式启动，工程施工中使用了如图18甲所示的某型号挖掘机运送沙土，该型号的挖掘机空载时的总质量是9t,每条履带与地面的接触面积是2.25㎡。在运送沙土中，它将装有1.8104N沙土的铲斗用4s的时间以2.4m/s的平均速度从图18乙中最低点A移送到最高点B，接着再用2s的时间沿水平方向移动4m将沙土卸到汽车上。求：
(1)挖掘机静止、空载且不工作时(如图甲所示)对水平地面的压强是多少帕?
(2)挖掘机在运送1.8104N沙土中对沙土做了多少焦耳的功?
(3)如果挖掘机在上述运送沙土过程中的平均功率为60kw，此过程挖掘机的机械效率是多少?
一、选择题(共36分，每小题2分)
题号******8
答案DBDDACADBDBABBDCDB
二、填空题(共14分，每空1分)
19.增大 不变 20.10 减小
21.8 竖直向上 22.大 受力面积小，压强大
23.连通器 上升 24.自身的重力 不变
25.转动摇把 定滑轮
三、实验探究题(第26题2分，第27题4分，第28题4分，第29题5分，计15分)
26.评分说明：正确画出F 的力臂L1(1 分)、重力G的示意图(1 分)
27、(1)二力平衡;
(2)甲和丙 接触面越粗糙;
(3)没有控制压力大小保持不变
28、(1)让力臂沿杠杆，便于直接从杠杆上读出力臂的大小;F1L1= F2
(2)1 变大
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