问题 实验题

(9分)某同学在做“研究匀变速直线运动”实验时,从打下的若干纸带中选出了如图所示的一条(每两点间还有4个点没有画出来),图中上部的数字为相邻两个计数点间的距离。打点计时器的电源频率为50Hz。

如果用s1、s2、s3、s4、s5、s6来表示各相邻两个计数点间的距离。由这些已知数据计算:该匀变速直线运动的加速度的表达式为a=__________________。其大小为a="___" _m/s2。与纸带上D点相对应的瞬时速度v="_________" m/s。(答案均要求保留3位有效数字)

答案

a=[(s4+s5+s6)-(s1+s2+s3)]/9T2.  1.93      1.39

题目分析:由逐差法得加速度表达式为(s4+s5+s6)-(s1+s2+s3)=a(3T)2,得a=[(s4+s5+s6)-(s1+s2+s3)]/9T2,带入数据求得a="1.93" m/s2。纸带上D点对应纸带的瞬时速度为CE间的平均速度,相邻计数点间时间为0.1s,求得D点对应速度为1.39m/s。

阅读理解

Dad came in the midnight. We heard every sound, but we pretended to be asleep.

Next morning he looked weak and thin, sitting in a chair by the kitchen fire. The light of the fire shone through his long empty sleeve. Everything went as usual. Grandma found something to do in the bedroom. Grandpa went out for some water. Mother, with her back to us, was getting the cakes ready for breakfast.

But nothing was right. When grandma came out of the bedroom, she walked on tiptoe. When grandpa came back, he said nothing about the weather. At breakfast Mother passed us the fruit and said something, but her voice was too high.

At last my sister, Lou, pushed back her chair. “It’s your turn to wash the dishes.” But I had washed the dishes the night before. I said nothing because it was not right to quarrel in front of Dad just home with the empty sleeve.

“It is your turn,” Lou said again. I looked at her in surprise.

“It is not,” I said because I suddenly remembered Mother had told us to go on as usual.

“Children, children,” Mother said in a quiet, glad kind of voice.

And Dad was smiling because he felt at home at last.

小题1:What do you know happened to Dad in the story?

A.He was badly ill.

B.He had a long journey.

C.He drank too much.

D.He lost one of his arms.小题2:The family        when they saw Dad’s empty sleeve.

A.was too surprised to do anything

B.felt sad and cried a lot

C.tried not to show their feelings

D.showed no worry at all小题3:From the story, we know          .

A.the two sisters often quarreled about who should wash the dishes

B.the family liked seeing the two sisters quarrelling after breakfast

C.Dad loved the two sisters very much though they often quarreled

D.Mother told the two sisters to quarrel with each other the night before小题4:Which of the following can be the best title of the story?

A.The Quarrelling Sisters

B.Dad Was Back

C.After the Accident

D.An Empty Sleeve

单项选择题