3.某实验小组采用图所示的装置探究“动能定理”,图中小车中可放置砝码,实验中,小车碰到制动装置时,钩码尚未到达地面,打点针时器工作频率为50 Hz.
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(1)实验的部分步骤如下:
①在小车中放入砝码,把纸带穿过打点计时器,连在小车后端,用细线连接小车和钩码;
②将小车停在打点计时器附近, , ,小车拖动纸带,打点计时器在纸带上打下一列点, ;
③改变钩码或小车中砝码的数量,更换纸带,重复②的操作。
(2)图是钩码质量为0.03 kg,砝码质量为0.02 kg时得到的一条纸带,在纸带上选择起始点0及A、B、C、D和E五个计数点,可获得各计数点到0的距离5及对应时刻小车的瞬时速度v,请将C点的测量结果填在表1中的相应位置.
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(3)在上车的运动过程中,对于钩码、砝码和小车组成的系统, 做正功,
做负功.
(4)实验小组根据实验数据绘出了图中的图线(其中Δv2=v2-v20),根据图线可获得的结论是 .要验证“动能定理”,还需要测量的物理量是摩擦力是 .
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表1纸带的测量结果
|
测量点 |
S/cm |
r/(m·s-1) |
|
0 |
0.00 |
0.35 |
|
A |
1.51 |
0.40 |
|
B |
3.20 |
0.45 |
|
C |
|
|
|
D |
7.15 |
0.54 |
|
E |
9.41 |
0.60 |
5.C 推理判断题。最后一段介绍:许多小学把写作课已规定为必修课,在大学里,要求学生交书面作业。由此我们可以得出结论:今后越来越多的学生会重视书写。故C项为正确答案。
4基础写作
假如你是John.在三鹿毒奶粉事件后在学校3000名学生中进行”每天你还喝牛奶吗”的调查活动。调查结果如下:
|
每天你还喝牛奶吗 |
比例 |
理由 |
|
喝 |
55% |
绝大部分牛奶质量可靠;牛奶可增强体质 |
|
不喝 |
32% |
对牛奶.尤其是国产牛奶失去信心;害怕得病 |
|
不确定 |
13% |
等待质量检测结果再定 |
[写作要求]
只能使用;5个句子表达全部的内容;
[评分标准]
句子结构准确.信息内容完整.篇章结构连贯:
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[答案]
After the publicity of the Sanlu contaminated milk powder issue, a survey was carried out among the 3, 000 students on "whether you still drink milk" in our school. The results are as follows. 55 percent of the students who participated in the survey give a positive answer, for they believe that the majority of milk products are reliable and can help people strengthen their body. Meanwhile, about one third of them express their doubts and refuse to drink any more milk in the future because of their loss of confidence in domestic milk and the fear of catching disease. The 13 percent left say that they won't make a decision before the results of the quality test are out.