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如图所示，A、B为真空中相距为d的一对平行金属板，两板间的电压为U，一带电粒子从A板的小孔进入电场，粒子的初速度可视为零，经电场加速后从B板小孔射出．已知带电粒子的质量为m，所带电荷量为q．带电粒子所受重力不计．求：

（1）带电粒子从B板射出时的速度大小；

（2）带电粒子在电场中运动的时间．

答案

（1）设带电粒子从B板射出时的速度为v，根据动能定理：

则有：

1
2
 mv2=qU

解得，v=

2qU
m

（2）以带电粒子为研究对象，设带电粒子在电场中运动的时间为t，根据运动学公式

设带电粒子在电场中的加速度为a，

由牛顿第二定律，F电=ma

又E=

U
d

且F电=qE

 解得：a=

qU
dm

由位移公式，d=

1
2
at2

解得：t=

2d
a
=d
2m
qU
  

答：（1）带电粒子从B板射出时的速度大小v=

2qU
m
；

（2）带电粒子在电场中运动的时间d

2m
qU
．

多项选择题

工程项目融资咨询按资金构成可分为（）。

A.货币资金

B.项目资本金

C.债务资金

D.吸收新股东

E.银行贷款
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填空题

Part 1


Questions 1-8


·Read the article below.
·Choose the best sentence from the list on the next page to fill each of the gaps.
·For each gap (1-8) mark one letter (A-H) on the Answer Sheet.
·Do not mark any letter twice.
Poll: Obama Seen As More Compassionate Than McCain
Just hours before the start of the second presidential debate, a new national survey suggests that Sen. Barack Obama is making gains among Americans as a compassionate candidate. (1)
In a new CNN/Opinion Research Corporation poll out Tuesday afternoon, 55 percent of registered voters questioned say that Obama "cares more about people like you" than Sen. John McCain, with 35 percent saying McCain cares more than Obam
  • a. (2)
    "The all-time champion of town-hall debates was Bill Clinton because he was able to connect with the audience members so well," said CNN polling director Keating Holland. "Voters nationwide seem to feel some connection with Obama. (3) John McCain has a pretty good track record at town halls, and it’s possible that he will be the one who looks more compassionate."
    Obama also appears to be building a lead as the candidate with the clearer plan to solve the country’s problems. He has a 15-point lead over McCain on that question in the poll, 48 percent to 33 percent. (4)
    Obama is also making gains on being a p and decisive leader. A 19-point McCain advantage early last month has now shrunk to a 5-point lead. (5)
    "Voters agree with McCain that things are going well for the U.S. in lraq. That’s a switch since April, when we last asked that question," Holland said. (6)
    Among voters, Obama also leads on who would better handle the economy, 57 percent to 37 percent; a financial crisis, 53 percent to 36 percent; and health care, 60 percent to 33 percent. (7)
    Obama’s favorable rating among those questioned in the poll is 62 percent, down one percentage point from three weeks ago. (8) A. But on the question of who has the better experience to be president, McCain still has a big lead over his rival, 54 percent to 36 percent.B. That could be important in the debate in Nashville, which is a town hall-style meeting with the candidates fielding questions from undecided voters in the audience.C. The question is whether he’ll connect with the people at the debate tonight.D. That 20-point margin for Obama is up from a 9-point advantage a month ago.E. McCain’s favorable rating is 54 percent, down three points from three weeks ago.F. "But voters also agree with Obama that the war was a bad idea—and they haven’t changed their minds on that in almost four years."G. McCain leads on the issue of terrorism, 54 percent to 44 percent.H. Last month, McCain had a 2-point advantage over Obama on the topic of having a clearer plan.
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