如图所示，在真空中水平放置的平行板电容器两板间的电压为U1=200_爱下问搜题

搜题请搜索小程序“爱下问搜题”

问题问答题

如图所示，在真空中水平放置的平行板电容器两板间的电压为U₁=200V，在距下板h=1.6cm的M点，带负电的液滴处于静止状态．如果使两板之间电压突然减小到U₂=100V，取g=10m/s2．则带电液滴运动到极板上需要经历的时间t为多少？

答案

设两板间距离为d，带电液滴的质量为m，当带负电的液滴处于静止状态时，

根据平衡条件得

q

U1

d

-mg=0

当两板间电压突然减小到U₂=100V时，带负电的液滴从静止开始向下做匀加速直线运动，设其加速度为a，则根据牛顿第二定律和运动学公式得

mg-q

U2

d

=ma

h=

1

2

at2

联立以上三式得

t=

2hU1

(U1-U2)g

=

2×1.6×10-2×200

(200-100)×10

s=0.08s

答：带电液滴运动到极板上需要经历的时间t为0.08s．

完形填空

It was 20 years ago. I was driving home with my 4-year-old son. Traffic was light. I was singing quietly along   36  the song playing on the radio. I   37  at the intersection and looked both ways. The road was   38 . I slowly started to make a right turn when suddenly a car rounded the curve at high speed and came   39  at me. I stomped (猛踩) on the brakes of my car killing the engine in the process. The speeder zoomed (疾驰) past my dead car   40  me by inches without even slowing down.
41  I knew it, a stream of rude words was flying from my lips,   42  after the car and its driver. I then saw my son who was staring up at me   43 . With a red face and a(an)   44  smile I started the car, pulled back onto the road, and headed home.
Later that evening I was reading a book when I heard certain   45  words coming from my son’s bedroom. He was replaying the   46   over and over in his mind. Too   47  I realized the   48  of those words that had flown from my lips in that moment of   49 . It took a lot of talks about good language and bad language with my son to undo (消除)the   50  of that incident.
That   51  , however, did teach me just how strong words   52  be. It helped me to decide to stop swearing (咒骂) in my own life and to start using words that uplift and inspire instead. I slowly realized that language is a   53  from God and should be used to make our world better but not worse. I learned    54  that a few loving words can help a hurting heart, strengthen a   55  spirit, and lighten a heavy load. I pray then that all of your words today are full of love, joy, happiness, and light.

D．approaching

B．embarrassed

A．challenging

选择题

2013年10月15日报道：长沙拟建垃圾焚烧厂，该项目建设内容包括建设六条850吨/日的垃圾焚烧生产线，每条垃圾焚烧生产线配置一套烟气净化系统；建设一套余热锅炉产生蒸汽用来发电，采用三台30MW中温中压凝汽式汽轮发电机组；配套建设附属生产、生活设施。预计2016年底左右，长沙首个垃圾焚烧厂将投产，一天可焚烧垃圾5000吨左右，届时长沙垃圾填埋将减量80%，每日能产生15万度电，解决4万至5万人一天的用电需求。据此，回答下列各题

小题1:关于建垃圾焚烧厂对长沙的影响，正确的是

A．解决了能源紧张状况　

B．改善了城市环境质量

C．加剧了人地矛盾

D．加大了空气污染小题2:影响这类工厂布局的主导因素是

A．原料

B．市场

C．技术

D．环境小题3:有关大力发展垃圾焚烧发电厂叙述正确的是

A．是未来城市生产生活主要能源

B．工业污染由城市转移到了乡村

C．有利于保护土地资源、水资源

D．给城市其它功能区带来严重污染