问题 选择题

一列简谐横波沿x轴正方向传播,t时刻波形图如图中的实线所示,此时波刚好传到P点,t+0.6s时刻的波形如图中的虚线所示,a、b、c、P、Q是介质中的质点,则以下说法正确的是(   )

A.这列波的波速可能为50m/s

B.质点a在这段时间内通过的路程一定小于30cm

C.质点c在这段时间内通过的路程可能为60cm

D.如果T=0.8s,则当t+0.5s时刻,质点b、P的位移相同

答案

ACD

分析:由图可知波的波长,而由两列波的波形图可得两波形相距的时间与周期的关系,则可得出波速的表达式;由波速可知周期的表达式,则可得出质点的路程及位移.

解答:解:A、由图可知,波的波长为40m;两列波相距0.6s=(n+)T,故周期T=; 

波速v=(4n+3)m/s=(4n+3),当n=0时,v=50m/s时,故A正确;

B、质点a在平衡位置上下振动,振动的最少时间为T,故振幅最小为30cm,故B错误;

C、c的路程为60cm说明c振动了1.5个周期,则可有:+1.5T=0.6,即+=0.6,解得,n=0时满足条件,故C正确;

D、在 t 时刻,因波沿X轴正方向传播,所以此时质点P是向上振动的,经0.5秒后,P是正在向下振动(负位移),是经过平衡位置后向下运动0.1秒;

而质点b是正在向上振动的(负位移),是到达最低点后向上运动0.1秒,因为0.2秒等于,可见此时两个质点的位移是相同的. 故D正确;

故选ACD.

点评:本题考查了波的多解性以及振动的性质,难度较大,特别要注意理解D答案中简谐运动的对称性,P和b正好处在了同一点,但是方向恰好相反.

单项选择题 B1型题
阅读理解

阅读下面短文,然后用英语简洁回答文后所给的问题(注意每题每小题要求的词数)。

     About 40 percent of the top students in college entrance examinations have chosen overseas universities

for their postgraduate studies, according to a survey.

     Most of them have stayed overseas after finishing their intended courses, showed a survey that tracked

130 top performers in college entrance exams from 1977 to 1998.

     The survey, released on the China Alumni Association website, found it worrying that many of the top

students would not _____ despite the country's rapid development in the past few decades.

     The government should find better ways to hold back talented students, said Cai Yanhou, a professor

with Central South University in Changsha, capital of Hunan Province.

     UNESCO figures show Chinese students consist of 14 percent of international students, the highest in

the world. Their favorite destinations for higher studies are the US, Britain and Japan. Some experts said

handsome scholarships, better job prospects and more opportunities to pursue further studies are the main

attractions of foreign universities.

     But Cai, who also led the survey team, said "top in exams" does not necessarily mean "top in career"

because the study found none of the top students at college entrance exams had become a top Chinese

expert or academic. Some of them are just more adaptable to exam-oriented education (应试教育) than

their peers, experts said.

     The media fill pages and time slots(逢) with their "success" stories to gain wider readership and

viewership. High schools promote their former students proudly to attract new ones, and universities

want to show their superior status by recruiting (吸收) them, they said.

     Wang hoped future reforms would do away with the score-oriented method so that students can be

judged from all aspects.

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

     _____________________________________________________________________________________

2. Which sentence in the passage can be replaced by the following one? The top students "success" stories

    are widely announced by the media to attract the readers' and the viewers' interest.

     _____________________________________________________________________________________

3. Please fill in the blank in the second paragraph with proper words or phrases to complete the sentence.

    (Please answer within 10 words) 

     _____________________________________________________________________________________

4. If you are one of the top students in college entrance examinations, will you choose to study abroad?

    Why or why not? (Please answer within 30 words)

     _____________________________________________________________________________________

5. Translate the underlined sentence into Chinese.

     _____________________________________________________________________________________