在验证机械能守恒定律的实验中，质量为1kg的重锤下落，通过打点_爱下问搜题

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问题实验题

在验证机械能守恒定律的实验中，质量为1kg的重锤下落，通过打点计时器在纸带上记录运动过程，打点计时器所接电源为6 V、50Hz的交变电源，纸带打点如下图所示．

纸带上O点为重锤自由下落时的打点起点(O、A间点未画出)，选取的计数点A、B、C、D依次间隔一个点(图中未画出)，各计数点与O点距离如图所示，单位为mm，重力加速度为9.8m/s²，则：（计算结果保留三位有效数字）

(1)打点计时器打下B点时，重锤速度v_B＝________，重锤动能E_kB＝________.

(2)从开始下落算起，打点计时器记录B点时，重锤势能减少量为________．

(3)由(1)(2)中数据可知，由重锤下落过程说明_______．误差原因可能是： _______．

答案

(1)1.18m/s；0.690 J　(2)0.692 J　

(3)机械能守恒；摩擦阻力等

题目分析：（1）做匀变速直线运动的物体，在t时间内的平均速度等于时刻的瞬时速度，设相邻计数点之间时间间隔为：，则有：，重锤动能为：；（2）从开始下落到记录B点时，重锤减少的重力势能为：。

（3）重锤下落过程中，在忽略摩擦力做功情况下，机械能守恒；动能变化小于重力势能变化，时由于摩擦力做功。

完形填空

In the morning, Slim got up and prepared breakfast for his wife as usual. Nicole, his wife was listening to music in the bedroom. __小题1:_, he felt that his body was shaking. Slim had the __小题2:__ response that there was an earthquake! He __小题3:__ quickly: “Dear, earthquake! Go to the toilet！” Nicole heard the shouting, 小题4: the first aid box quickly and ran into the toilet. The house was 小题5: even more dramatically (剧烈地)．
Bathroom was the next door to the kitchen. Slim picked up a kitchen __小题6:__ and two pieces of bread outside the kitchen. Slim tried to __小题7:__ along the wall to help Nicole.__小题8:__, it got dark suddenly with an explosion. The house __小题9:_____down and many things fell from above. Nicole was quickly buried in 小题10: .She felt breathing very difficult. She tried to stand up, but 小题11:  .
A few minutes later, the land was __小题12:.Nicole heard the sound of short __小题13:_ and thought it was Slim! She shouted to him but no __小题14:__！ He probably fainted. Nicole kept saying his name and she finally heard a response, two people encouraged and __小题15:__ each other. They knew that there must be a way to   小题16: .
Slim found that they were close and were   小题17:  by the fallen stones and some powder. He started to dig with the kitchen knife. He felt __小题18:__ from his fingers. Finally, he removed the last piece of larger stones. Slim touched Nicole's one hand, then dug the __小题19:__ stones of her body. Finally, Nicole had a __小题20:__ breathing slowly. Two people sat on the ground and hugged together.

C．Unfortunately

C．impractical

B．communicate

C．surrounding

单项选择题

下列哪一项不符合AIDP的临床表现（）

A.少数可呈面瘫

B.病前1～4周有感染史

C.四肢对称性下运动神经元瘫

D.腱反射亢进

E.肌强力常降低