问题 多选题

一辆车由甲地出发,沿平直公路开到乙地刚好停止,其速度图象如图所示,那么0-t和t-3t两段时间内,下列说法正确的是(  )

A.加速度大小之比为2:1

B.位移大小之比为1:2

C.平均速度大小之比为1:2

D.3t时刻回到出发点

答案

设物体的最大速度为v.

A、0-t时间内物体的加速度大小a1=

△v
△t
=
v
t

  t-3t时间内物体的加速度大小a2=

△v
△t
=
v
2t

  则a1:a2=2:1  故选A

B、0-t时间内物体的位移x1=

1
2
vt,t-3t时间内物体的位移x2=
1
2
v•2t
=vt.则x1:x2=1:2

C、0-t时间内物体的平均速度

.
v1
=
v
2
,t-3t时间内物体的平均速度
.
v2
=
v
2
.故C错误.

D、物体的速度均为正值,说明物体一直向正方向做单向直线运动,不可能回到出发点.故D错误.

故选AB

单项选择题 A1/A2型题
完形填空
When we read books we seem to enter a new world.  This new world can be similar to the one we are living in, or it can be very    1   .  Some stories are told    2   they were true.  Real people who live in a normal world do real things; in other words, the stories are about people just like us doing what we do.  Other stories, such as the Harry Potter books, are not    3   .  They are characters and creatures that are very different from us and do things that would be   4 for us.
But there is more to books and writing than this.  If we think about it, even realistic writing is only    5   .  How can we tell the difference between what is real and what is not real?  For example, when we read about Harry Potter, we do seem to learn something about the real world.  And when Harry studies magic at Hogwarts, he also learns more about his real life than    6   .  Reading, like writing, is an action.  It is a way of    7   .  When we read or write something, we do much more than simply look at words on a page.  We use our    8   --- which is real --- and our imagination ---which is real in a different way --- to make the words    9   in our minds.
Both realism and fantasy use the imagination and the “magic” of reading and writing to make us think.  When we read    10   realistic, we have to imagine that the people we are reading about are just like us, even though we know that we are real and they are not.  It sounds   11   , but it works.  When we read, we fill in missing information and    12   about the causes and effects of what a character does.  We help the writer by pretending that what we read is like real life.  In a way, we are writing the book, too.
Most of us probably don’t think about what is going on in our    13   when we are reading.  We    14   a book and lose ourselves in a good story, eager to find out what will happen next.  Knowing how we feel    15   we read can help us become better readers, and it will help us discover more about the real magic of books.
小题1:
A.possibleB.easyC.newD.different
小题2:
A.thatB.what C.whetherD.as if
小题3:
A.realisticB.reasonableC.moralD.instructive
小题4:
A.difficultB.impossibleC.importantD.necessary
小题5:
A.thinkableB.designedC.imaginedD.planned
小题6:
A.lessons B.dreamsC.experienceD.magic
小题7:
A.workingB.thinkingC.understandingD.living
小题8:
A.knowledgeB.skillC.wordsD.grammar
小题9:
A.come to life B.come to lightC.come to the pointD.come to nothing
小题10:
A.a newspaper B.somethingC.everythingD.a story
小题11:
A.dangerousB.seriousC.strangeD.terrible
小题12:
A.talkB.learnC.readD.think
小题13:
A.mindB.lifeC.worldD.society
小题14:
A.turn upB.pick upC.cook upD.bring up
小题15:
A.whatB.howC.whenD.why