问题 选择题

如图所示是一种升降电梯的示意图,A为载人箱,B为平衡重物,它们的质量均为M,上下均有跨过滑轮的钢索系住,在电动机的牵引下使电梯上下运行。已知电梯中所载人的质量为m,匀速上升的速度为v,在电梯到顶层前关闭电动机,电梯依靠惯性还能上升h的高度而停止。不计钢索与滑轮之间的摩擦,关于电梯配平衡重物的主要目的和上升高度h,下列说法正确的是:

A.电梯配平衡重物的主要目的是为了电梯上下运行时稳定些

B.电梯配平衡重物的目的是为了电梯上下运行时,电动机少做功

C.

D.h>

答案

BD

题目分析:平衡物与载人箱子质量相等,电梯运行时,电动机只需对载人箱中的人做功即可,B正确;关闭电动机后,载人箱和平衡物重力相平衡,电梯中所载的人的重力使整个系统减速,有mg=(m+2M)a,得a<g,则电梯上升高度h>v2/2g,D正确。

选择题
完形填空

第二部分:语言知识及运用(共两节,满分35分)

第一节:完形填空(共10小题;每小题2分, 满分20分)      

阅读下面短文,从各题所给的四个选项A、B、C、D中选出最佳选项。

The guitar is one of the oldest instruments known to man. It   21   originated in the vicinity of (在……附近) China. There were guitars in ancient Egypt and Greece as well, but the   22   history of the guitar started in Spain in the 13th century. By 1500 the guitar was   23   in Italy, France, and Spain. A French document of that time   24   that many people were playing the guitar. Stradivarius, the famous king of violin makers, could not resist   25   a variety of guitars. Also, there was no lack of music written for the instrument. Haydn, Schubert, and others   26   guitar music. When Beethoven was asked to compose music for the guitar, he went into a rage(大怒) and   27  , but eventually even Beethoven could not ignore the   28  .Legend tells us he finally called the guitar a miniature orchestra. Indeed the guitar does   29   like a little orchestra! Perhaps that is why in rural areas around the world the guitar has been a source of   30   for millions to enjoy.

21. A. certainly             B. mainly                     C. probably           D. partly

22. A. written                      B. learned              C. found                D. spoken

23. A. acceptable           B. popular            C. familiar             D. available

24. A. predicted            B. warned              C. denied               D. recorded

25. A. destroying           B. accusing            C. creating             D. following

26. A. enjoyed                     B. wrote                C. accepted            D. commented

27. A. refused               B. accepted            C. failed                D. escaped

28. A. contribution        B. challenge           C. history                     D. suggestion

29. A. look                   B. feel                   C. taste                  D. sound

30. A. intelligence         B. energy                     C. music                D. spirit