问题 问答题

.如图1-7所示,长为2L的板面光滑且不导电的平板小车C放在光滑水平面上,车的右端有块挡板,车的质量mC="4" m,绝缘小物块B的质量mB="2" m.若B以一定速度沿平板向右与C车的挡板相碰,碰后小车的速度总等于碰前物块B速度的一半.今在静止的平板车的左端放一个带电量为+q、质量为mA=m的小物块A,将物块B放在平板车的中央,在整个空间加上一个水平方向的匀强电场时,金属块A由静止开始向右运动,当A以速度v0B发生碰撞,碰后Av0/4的速率反弹回来,B向右运动.

小题1:求匀强电场的场强大小和方向.

小题2:若A第二次和B相碰,判断是在BC相碰之前还是相碰之后?

小题3:A从第一次与B相碰到第二次与B相碰这个过程中,电场力对A做了多少功?

答案

小题1:E= 方向水平向右

小题2:因sAL,故A第二次与B相碰必在BC相碰之后

小题3:W=qEL=mv02.

小题1:对金属块A用动能定理qEL=mv02

所以电场强度大小E= 方向水平向右

小题2:AB碰撞,由系统动量守恒定律得

mAv0=mA(-v0)+mBvB

mB=2m代入解得vB=v0

B碰后做匀速运动,碰到挡板的时间tB=

A的加速度aA=

AtB段时间的位移为

sA=vatB+atB2=-v0···(2=L

sAL,故A第二次与B相碰必在BC相碰之后

小题3:BC相碰,由动量守恒定律可得

mBvB=mBvB′+mCvC′  vC′=vB  vB′=0

A从第一次相碰到第二次与B相碰的位移为L,因此电场力做的功

W=qEL=mv02.

单项选择题 A1型题
完形填空
He drove after drinking alcohol, having a severe accident and had to get his arms removed.Since then, he has had to __31__ on his younger brother, who became his shadow, never leaving him alone for years. Except for writing with his toes, he was totally unable to do __32__ else. As the two brothers grew up together, they had their own problems and would often __33__. Finally, his younger brother went away and lived __34__, leaving him heartbroken and at a loss what to do.
__35__, a misfortune befell(降临)a girl. One night she was preparing dinner when the kerosene light on the stove was overturned, __36__ in a fire which took her hands away. Having decidedly __37__ her sister’s willingness to help her, she determined to be thoroughly __38__. At school, she always studied hard.Most of all she learned to be self-reliant. “I am lucky. Though my __39__ are broken, my heart can still fly.” she wrote in her blog.
One day, the young man and the girl were both invited to a(n)__40__ programme. The boy told the television hostess about his __41__ future, whereas the girl was full of __42__ for her life. They were both asked to write something on a piece of paper with their __43__. The boy: My younger brother’s arms are my arms. The girl: Broken wings, flying heart.
They had both gone through the same ordeal(痛苦经历), but their different __44__   determined the nature of their lives. As seems the case, __45__ disasters can strike our life at any time. How you handle the __46__ when faced with it is the true __47__  of your character. If you choose to __48__ or escape from the ordeal, it will follow you wherever you go. But if you decide to be strong, the __49__ will turn out to be a fortune on which new __50__will arise.
小题1:
A.liveB.standC.relyD.assist

1,3,5

 
小题2:
A.somethingB.everythingC.nothingD.anything

小题3:
A.quarrelB.shareC.supportD.dislike
小题4:
A.happilyB.lonelyC.separatelyD.disappointedly
小题5:
A.UnfortunatelyB.UnexpectedlyC.SimilarlyD.Naturally
小题6:
A.leadingB.bringingC.causingD.resulting
小题7:
A.turned toB.turned downC.turned offD.turned against
小题8:
A.aloneB.freeC.independentD.successful
小题9:
A.armsB.wingsC.dreamsD.promises
小题10:
A.interviewB.radioC.sportsD.health
小题11:
A.hopefulB.uncertainC.brightD.miserable
小题12:
A.calmnessB.enthusiasmC.patienceD.excitement
小题13:
A.handsB.strengthC.toesD.mouths
小题14:
A.charactersB.desiresC.opinionsD.attitudes
小题15:
A.unexpectedB.passiveC.roughD.serious
小题16:
A.emergencyB.misfortuneC.difficultyD.accident
小题17:
A.testB.reflectionC.displayD.problem
小题18:
A.ignoreB.resistC.complainD.suffer
小题19:
A.problemB.resultC.failureD.hardship
小题20:
A.solutionsB.waysC.rewardsD.hopes