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问题 问答题

在“测定匀速直线运动的加速度”实验中，得到一条纸带如下所示图．

纸带上的A、B、C、D、E、F是计数点（相邻两计数点之间还有四个点未画出）．打点计时器接在频率为50赫兹的低压交流电源上．已知AB=3.00厘米，BC=4.20厘米，CD=5.40厘米，DE=6.60厘米，EF=7.80厘米，FG=9.00厘米．则小车做匀变速直线运动的加速度a=______m/s2，在打点计时器打下B点时，小车运动的速度VB=______m/s．

答案

相邻两计数点之间还有四个点未画出，所以相邻的计数点间的时间间隔T=0.1s，根据匀变速直线运动的推论公式△x=aT2可以求出加速度的大小，

得：x4-x1=3a1T2

x5-x2=3a2T2

x6-x3=3a3T2

为了更加准确的求解加速度，我们对三个加速度取平均值

得：a=

1
3
（a1+a2+a3）

即小车运动的加速度计算表达式为：

a=

x6+x5+x4-x3-x2-x1
9T2
=
DG-AD
9T2
=
(9.00+7.80+6.60-5.40-4.20-3.00)×10-2
9×0．12
=1.20m/s2

根据匀变速直线运动中时间中点的速度等于该过程中的平均速度，

vB=

xAC
2T
=
(3.00+4.20)×10-2
2×0.1
m/s=0.36m/s

故答案为：1.20，0.36

选择题

I promised to get there before 5 o’clock, but now the rain is pouring down. They ______ for me impatiently.

A．may wait

B．ought to wait

C．could wait

D．must be waiting
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单项选择题

What’s your earliest childhood memory Can you remember learning to walk Or talk The first time you heard thunder or watched a television program Adults seldom (1) events much earlier than the year or so before entering school, (2) children younger than three or four (3) retain any specific, personal experiences.

A variety of explanations have been (4) by psychologists for this "childhood amnesia". One argues that the hippo-campus; the region of the brain which is (5) for forming memories, does not mature until about the age of two. But the most popular theory (6) that, since adults don’t think like children, they cannot (7) childhood memories. Adults think in words, and their life memories are like stories or (8) one event follows (9) as in a novel or film. But when they search through their mental (10) for early childhood memories to add to this verbal life story, they don’t find any that fit the (11) . It’s like trying to find a Chinese word in an English dictionary.

Now psychologist Annette Simms of the New York State University offers a new (12) for childhood amnesia. She argues that there simply aren’t any early childhood memories to (13) . According to Dr. Simms, children need to learn to use someone else’s spoken description of their personal (14) in order to turn their own short-term, quickly forgotten (15) of them into long-term memories. In other (16) , children have to talk about their experiences and hear others talk about (17) --Mother talking about the afternoon (18) looking for seashells at the beach or Dad asking them about their day at Ocean Park. Without this (19) reinforcement, says Dr. Simms, children cannot form (20) memories of their personal experiences.

Notes: childhood amnesia 儿童失忆症。

18（）

A.taken

B.utilized

C.applied

D.spent
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