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问题 多选题

在同一均匀介质中，分别位于x=-2m和x=15m处的两波源s1、s2，产生两列沿x轴相向传播的横波，振幅均为A=2cm，已知波源s1的振动周期为1s，t=0时刻介质中刚好形成如图两列波的波形，正确的是 （　　）

A．波源s2产生的波的波速为4m/s

B．波源s2比波源s1振动早1s，且两波源的起振方向相同

C．t=0.75s时刻，质点P的位移为-2cm

D．t=1.25s以后，质点P的位移总为0

答案

A、由v=

λ
T
可得两列波的波速v=
4m
1s
=4m/s，故A正确；

B、两列波波速相同，s2传播的距离比s1多传播4m，故s2的波源起振时间早△t=

4m
4m/s
=1s，由上下坡法知波源的起振方向均为向下，故B正确；

C、t=0.75s=

3
4
T1时刻，t=0时x=1m处质点的振动形式传播到P，s2上t=0时刻的x=7m处质点的振动形式传播到P，则P点的位移为：-2cm+0=-2cm，C正确；

D、t=1.25s以后，P质点不是波峰与波谷相遇，故不是振动减弱点，则其位移不是总为零，故D错误；

故选：ABC．

完形填空

第二节   完形填空（共20小题，每小题1分，满分20分）

I am a mother of three，and have recently completed my college degree．The last class I had to  36 was Sociology．The teacher’s last  37 of the term was called“Smile．”The class was asked to  38 and smile at three people．My husband，youngest son and I headed for McDonald’s．It was just our  39 of sharing special playtime with our son．We were standing in line，waiting to be 40  when all of a sudden everyone around us began to back away and then 41  my husband did．

I sensed a 42 smell and turned around．and there 43  behind me were two poor homeless men．As I 4 4 down at the short gentleman 4 5  to me，he was“smiling”．The second man rubbed his hands stupidly as he stood   46  his friend．   。

I was so touched by the   47 that I held my tears as I stood there with them．The young lady at the 48 asked him what they wanted．He said，“Coffee is all，Miss；”because that was all they could  49 ．Then I smiled and asked the young lady behind the counter to give me two more breakfast meals on a  50  tray．Then I walked to the table that the men had chosen as a resting spot．I put the tray on the table and   51  my hand on the blue-eyed gentleman’s cold hand．He looked up at me，with   52  in his eyes，and said，“Thank you．”I started to cry as I walked away to  53 my husband and son．

I returned to my  54 on the last evening of class，with this story in hand．I turned in“my project”．I   55 with one of the biggest lessons I would ever learn．

36．A．teach           B．attend                 C．pass                D．turn

3 7．A．goal           B．paper                C．project            D．degree

38．A．get together   B．go out                C．stay inside       D．keep calm

39．A．field            B．way                    C．chance            D．interest

40．A．served         B．charged               C．expected         D．ordered

41．A．only            B．even                   C．just                 D．still

42．A．good           B．stressful              C．horrible          D．pleasant

43．A．standing      B．falling                C．1ying              D．sitting

44．A．threw          B．headed                C．looked            D．seated

45．A．generous      B．close              C．friendly          D．similar

46．A．before         B．behind                C．after                  D．over

47．A．smell           B．condition        C．health         D．smiles

48．A．counter        B．chair                  C．door                  D．table

49．A．eat              B．afford                 C．find                D．cook

50．A．separate       B．beautiful             C．large               D．expensive

51．A．laid             B．set                      C．caught            D．stuck

52．A．smiles         B．surprises             C．pities              D．tears

53．A．search         B．join                    C．invite              D．get

54．A．home                 B．job                     C．college            D．work

55．A．dealt           B．did                     C．graduated        D．dropped
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单项选择题

所谓管线（pipeline）
是指？（）

A.将一个程序的输出作为某一个程序的输入

B.资料流

C.I/Obuffer

D.memory buffer
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