问题 选择题

如图7所示,把能在绝缘光滑水平面上做简谐运动的弹簧振子放在水平向右的匀强电场中,小球在O点时,弹簧处于原长,A、B为关于O对称的两个位置,现在使小球带上负电,并让小球从B点静止释放,那么下列说法正确的是(  )

A.小球仍然能在A、B做简谐运动,O点是其平衡位置

B.小球从B运动到A的过程中,动能一定先增大后减小

C.小球不可能再做简谐运动

D.小球从B点运动到A点,其动能的增加量一定等于电势能的减小量                                      

答案

答案:D

当弹簧弹力等于电场力时为平衡位置,此时弹簧被压缩,平衡位置不再是O点,所以A错;由于B点的弹簧弹力大小与电场力大小关系未知,所以也无法判断A点两力关系,动能变化情况无法判断,B错;小球在电场力和弹力作用下依然做简谐运动,C错;

单项选择题 共用题干题
阅读理解

阅读表达。

     One of the most popular things at Lingan University of Hong Kong is "Breakfast with the President" which

aims to break down student-faculty barriers (障碍). Every week, President Chen Kwan-yin invites students

to have breakfast with him. Because of the small number of 2,000 students, almost every student can get two

or three chances to do it during their three years' study. All they need to do is to add their names on the waiting

list. The breakfast starts at 8:00 a.m. You are warned not to be late because President Chen _____. It is a round

table breakfast of about l0 people. Everybody has a card with their name and major on. Chen asks students to

introduce themselves and then have breakfast, along with a casual talk about their life at the university. He is

kind to students and open to any complaints or suggestions.

     Many students come to the breakfast with problems to be settled. It is said that any reasonable requests and

suggestions raised during the breakfast will be taken care of. When my own "Breakfast with the President"

came, I was very nervous and excited. I got up early that morning. The president was dressed formally, but

what he said to relax us showed he was an easy-going person.

     Then he asked me about my exchange student life and what he could do to help me. He also discussed with

us many of his dreams for the university's future. He was a very special president, more like a friend. After the

breakfast, I greet him warmly whenever we meet, as every student on campus does.

1. What is the best title of the passage? (Please answer within 10 words.)

    _____________________________________________________________________________________

2. Try to find some words from the passage to describe the president. (Please give at least 3 words.) 

    _____________________________________________________________________________________

3. Suppose you will have breakfast with the president tomorrow morning, what will you prepare? (Please

    answer within 30 words.)

    _____________________________________________________________________________________

4. Please fill in the blank with proper words or phrases. (Please answer within 5 words.) 

    _____________________________________________________________________________________

5. Translate the underlined sentence into Chinese. 

    _____________________________________________________________________________________