在做“研究平抛运动”的实验时，让小球多次沿同一轨道运动，通过_爱下问搜题

搜题请搜索小程序“爱下问搜题”

问题填空题

在做“研究平抛运动”的实验时，让小球多次沿同一轨道运动，通过描点法画小球做平抛运动的轨迹．为了能较准确地描绘运动轨迹，下面列出了一些操作要求，将你认为正确的选项前面的字母填在横线上______．

a．通过调节使斜槽的末端保持水平

b．每次释放小球的位置必须相同

c．每次必须由静止释放小球

d．记录小球位置用的铅笔每次必须严格地等距离下降

e．小球运动时不应与木板上的白纸（或方格纸）相接触

f．将球的位置记录在纸上后，取下纸，用直尺将点连成折线．

答案

a、通过调节使斜槽末端保持水平，是为了保证小球做平抛运动．故a正确．

b、因为要画同一运动的轨迹，必须每次释放小球的位置相同，且由静止释放，以保证获得相同的初速度．故bc正确．

d、因平抛运动的竖直分运动是自由落体运动，在相同时间里，位移越来越大，因此木条（或凹槽）下降的距离不应是等距的，故d错误；

e、实验要求小球滚下时不能碰到木板平面，避免因摩擦而使运动轨迹改变，最后轨迹应连成平滑的曲线．故f错误，e正确．

故选a、b、c、e．

选择题

去年暑假期间，张明与同学结伴去重庆旅游，他一路享受的方便条件，哪一项属于第三次科技革命的成果[ ]

A．乘火车到达武汉

B．乘轮船游览三峡

C．发电子邮件向父母报平安

D．乘飞机从重庆返回济南

完形填空

One evening I was resting in a cafe. I 36 a pair of newly bought white leather shoes, which were rather expensive. Then a boy came to me.
He was in a(n) 37 shirt, looking pale and about eleven. No sooner had I begun to speak than he opened the 38 in his hand and took out the tools of shoe-polishing. He 39 down, took off my leather shoes, and began to shine them.
He was busy doing his work 40 heavy rain began to pour down. People rushed to the café for 41 from the rain. More and more people crowded 42 and gradually separated the boy from me.
Hours passed, and it turned 43 . I had no shoes on my feet and 44 where the boy had been. I thought he would not 45 my shoes, and I would have to go home on my bare feet.
When it was near midnight the 46 ended, and there were fewer and fewer people in the café. The café was to be 47 . I had to move to the door, head 48 . just as I went to the gate, I 49 found that a boy of about eleven, looking very familiar, was sleeping at the 50 with his head leaning against a box and his upper body being 51 . he held a package made of his shirt tightly in his arms..
I shook him slightly and woke him up. He 52 up and rubbed his eyes for a while before he recognized me. Then he opened the package 53 , gave me my leather shoes, and apologized to me shyly. I 54 him and wrapped him with his unfit shirt, which had wrapped my leather shoes. On my way home, the 55 of the boy stayed in my mind.

D．preparation

B．surprisedly

D．immediately