问题 问答题

(1)请观察如图所示的订书机结构,指出其中用到了哪些力学知识,并举出两例填写到下面的表格内.

订书机结构应用的物理知识
例:压柄做得宽大增大受力面积,减小压强
(2)订书时,若订书针对书产生的压强为1×108Pa,订书针与书的接触面积为2×10-7m2,人手按压柄的压力为______N.(不考虑压柄的重力和摩擦)

答案

订书机是以转轴为支点的杠杆;

压柄做得比较宽是为了增大受力面积来减小对手的压强;

底座做得比较宽是为了增大受力面积来减小对桌面的压强;

钉尖做得尖是为了减少受力面积来增大压强;

故答案见下表:

订书机结构应用的物理知识
例:压柄做得宽大增大受力面积,减小压强
钉尖做得尖为了减少受力面积来增大压强
底座做得比较宽为了增大受力面积来减小对桌面的压强
(2)已知P=1×108Pa,S=2×10-7m2

由P=

F
S
可得人手按压柄的压力F=PS=1×108Pa×2×10-7m2=20N.

故答案为:20.

完形填空
Once my mother told me a story that in Africa, when an antelope (羚羊) wakes up every morning, the first thing it thinks about is, “I must be 36 to run faster than the fastest lion, or I will be killed.” 37 , a lion wakes from his dream. The first thing the lion thinks about is, “I must be able to catch the 38 antelope, or I will starve to 39 .” So almost simultaneously(同时地), the antelope and the lion get up and start running toward the 40 sun.
This is 41 : full of chances and challenges. Whether you are an antelope or a lion, you must go 42 when the sun rises. For students, it is just the same. If we don’t study hard, sooner or later, we will 43 the other students. At first I didn’t know what the word “exam” 44 . Later, I knew an exam was a kind of 45 . In competitions, there are always winners and 46 . As I grew up, I got to know competition well. In one’s life, there must be competitions, so people can 47 .
Each time I saw children playing games and heard their 48 , I wished I were that age again.  49 , I remembered my parents’ words: You must work very hard for a good future. So I 50 my pen and began to study hard again.
I was still not sure what competition 51 meant. One day, I was 52_in an English-speaking competition. When I went to the stage, I saw other students looking at me kindly. Suddenly I 53 what competition was. It is not as cruel as my teacher and parents told me. In fact, competition is the 54 : it is kind and necessary.
I learned a lot from realizing this 55 . Now I understand better about the world. Competition is important for us all.
小题1:
A.ableB.willingC.readyD.eager
小题2:
A.On the contraryB.At the same timeC.In other wordsD.In the first place
小题3:
A.fastestB.weakestC.slowestD.strongest
小题4:
A.deathB.survivalC.diseaseD.suffering
小题5:
A.sinkingB.settingC.shiningD.rising
小题6:
A.ruleB.lifeC.studyD.exam
小题7:
A.overB.throughC.aheadD.beyond
小题8:
A.fall behindB.pass byC.catch upD.hold back
小题9:
A.feltB.meantC.referredD.doubted
小题10:
A.victoryB.defeatC.processD.competition
小题11:
A.competitorB.playersC.losersD.failures
小题12:
A.improveB.concludeC.acquireD.handle
小题13:
A.cryingB.laughterC.whisperD.delight
小题14:
A.HoweverB.ThereforeC.BesidesD.Otherwise
小题15:
A.put upB.brought upC.made upD.picked up
小题16:
A.commonlyB.simplyC.obviouslyD.really
小题17:
A.succeedingB.participatingC.takingD.getting
小题18:
A.doubtedB.acknowledgedC.knewD.admitted
小题19:
A.toughB.importantC.contentD.opposite
小题20:
A.experienceB.knowledgeC.factD.consequence
单项选择题