问题 问答题

如图所示,电荷量为-e,质量为m的电子从A点沿与电场垂直的方向进入匀强电场,初速度为v0,当它通过电场中B点时,速度与场强方向成150°角,不计电子的重力,求:

(1)电子经过B点的速度多大;

(2)AB两点间的电势差多大.

答案

(1)电子垂直进入匀强电场中,做类平抛运动,B点的速度 v=

v0
cos60°
=2v0

(2)电子从A运动到B由动能定理得:

-eUAB=

1
2
mv2-
1
2
m
v20

A、B两点间的电势差 UAB=

1
2
m(2v0)2-
1
2
m
v20
-e
=-
3m
v20
2e

答:

(1)电子经过B点的速度为2v0

(2)AB两点间的电势差为-

3m
v20
2e

单项选择题
阅读理解

Among various programs, TV talk shows have covered every inch of space on daytime television. And anyone who watches them regularly knows that each one is different in style(风格). But no two shows are more opposite in content, while at the same time standing out above the rest, than the Jerry Springer and the Oprah Winfrey shows.

Jerry Springer could easily be considered the king of “rubbish talk”. The contents on his show are as surprising as can be. For example, the show takes the ever-common talk show titles of love, sex, cheating, and hate, to a different level. Clearly, the Jerry Springer show is about the dark side of society, yet people are willing to eat up the troubles of other people’s lives.

Like Jerry Springer, Oprah Winfrey takes TV talk show to its top. But Oprah goes in the opposite direction. The show is mainly about the improvement of society and different quality(质量) of life. Contents are from teaching your children lessons, managing your work week, to getting to know your neighbors.

Compared to Oprah, the Jerry Springer show looks like poisonous waste being poured into society. Jerry ends every show with a “final word”. He makes a small speech about the entire idea of the show. Hopefully, this is the part where most people will learn something very valuable.

Clean as it is, the Oprah show is not for everyone. The show’s main viewers are middleclass Americans. Most of these people have the time, money, and ability to deal with life’s tough problems. Jerry Springer, on the other hand, has more of a connection with the young adults of society. These are 18-to-21-year-olds whose main troubles in life include love, relationship, sex, money and drug. They are the ones who see some value and lessons to be learned through the show’s exploitation.

小题1:Compared with other TV talk shows, both the Jerry Springer and the Oprah Winfrey are ______.

A.more interesting.

B.very popular.

C.more detailed.

D.more formal.小题2:Though the social problems Jerry Springer talks about appear unpleasant, people who watch the shows ______.

A.remain interested in them.

B.are ready to face up to them.

C.remain cold to them.

D.are willing to get away from them.小题3:Which of the following is likely to be a topic of the Oprah Winfrey show?

A.A new type of robot.

B.Nation hatred(憎恨).

C.Family income planning.

D.Street accident.小题4:We can learn from the passage that the two talk shows ______.

A.have become the only ones of its kind.

B.exploit the weaknesses in human nature.

C.appear at different times of the day.

D.attract different people.