问题 问答题

如图所示, 三个台阶每个台阶高 h="0.225" 米,宽s=0.3米。小球在平台AB上以初速度v0水平向右滑出,要使小球正好落在第2个平台CD上,不计空气阻力,求初速v0范围。某同学计算如下:(g取10m/s2)

根据平抛规律          2h=gt2/2 ;      

到达D点小球的初速     vD =2s/t=2×0.3/0.3=2m/s

到达C点小球的初速     vC =s/t=0.3/0.3=1m/s

所以落到台阶CD小球的初速范围是   1m/s < v0 < 2m/s

以上求解过程是否有问题,若有,指出问题所在,并给出正确的解答。

答案

以上解题有问题,小球无法到达C点。1.4m/s < v0 < 2m/s

以上解题有问题,小球无法到达C点。

若要小球恰好落在CD上的最小速度应是小球恰好从F点擦过,落在CD上

所以最小速度:

所以:  1.4m/s < v0 < 2m/s

该同学的临界条件找的不准导致错误,很明显小球不能到达C只能从F的边缘擦过。

完形填空

Engagement, wedding, and birth of a baby are the three steps of a new family. The Danes’ special ways of doing these things inform their native culture.

People in other places of the world usually give their lovers a finger ring or a bundle of flowers as a gift of engagement.   36  in some areas of Denmark, it is still considered   37  

for a young man to   38  his fiancée with the wooden clappers once used to   39  clothes

  40  in a stream. These clappers were engraved with love-poems, and   41  tradition, they ensured good fortune and happiness.

And their country weddings also show a tint of local convention(传统). Until recently, a Danish country wedding was an event which   42  all who lived in the surrounding   43 . Everyone was tacitly(不言而喻地) invited to celebrate with the young couple. Preparations for the wedding lasted for many days but were made   44 , because to show happiness openly   45 

arouse the anger and jealousy of evil spirits.

46  the wedding morning the couple met in the courtyard of the bride’s house. The relatives and friend presented themselves to the couple, bowed and placed gifts at their feet. Every gift was   47  by good wishes recited in prose(散文) or in verse;   48  modest the gift the more elaborate(精致的) the wishes had to be.   49  who had neither the means to give   50 

the imagination to make a speech were, as a sign of their goodwill, placed   51  guard over the presents and, in the evening, over the couple’s bed.

  52  the conclusion of the ceremony a large jar of beer was taken to the courtyard. The hands of the betrothed(已订婚的) were joined over the jar and it was   53  into fragments(碎片). These pieces were picked   54  by the girls of marriageable age who were present, the girl with the largest   55  being destined to marry first.

36.A.However             B.But                     C.Therefore            D.So

37.A.a luck                 B.luck                    C.lucky                  D.lucks

38.A.send                   B.present                C.bring                  D.give

39.A.strike                  B.beat                    C.hit                      D.blow

40.A.to wash               B.washed                C.to be washed        D.washing

41.A.according to        B.with a view to      C.so far as              D.in addition to

42.A.stated                  B.related                C.concerned            D.considered

43.A.area                    B.district                C.zone                   D.region

44.A.publicly              B.silently                C.unknowingly       D.secretly

45.A.would                 B.should                 C.must                   D.may

46.A.At                     B.In                       C.On                      D.To

47.A.completed           B.accompanied        C.accomplished       D.matched

48.A.much more          B.the more             C.any more             D.more

49.A.These                  B.Those                  C.People                D.They

50.A.or                       B.and                     C.nor                     D.then

51.A.in                       B.on                      C.at                       D.against

52.A.At                      B.In                       C.To                      D.For

53.A.smashed(弄碎)    B.ruined                 C.crashed               D.cracked

54.A.out                     B.up                      C.on                      D.at

55.A.part                    B.fragment             C.section                D.block

填空题