问题 选择题

如图是小朋友玩蹦蹦床的情景,对他们在上升和下落过程中机械能的变化,下列分析不正确的是

A.小孩上升到最高点时的重力势能最大

B.没有接触蹦床前,下落的过程中重力势能转化为动能

C.小孩下落到最低点时蹦蹦床的弹性势能最大

D.小孩下落到最低点时的动能最大

答案

答案:D

题目分析:重力势能跟高度有关,小孩上升到最高点时,高度最大,重力势能最大,A对,动能跟速度有关,没有接触蹦床前,下落的过程中速度在增大,高度在减小,故下落的过程中重力势能转化为动能,B对,小孩下落到最低点时弹簧压缩的最多,故这时蹦蹦床的弹性势能最大,C对,小孩下落到最低点时,速度为0,故D错。

完形填空

Everyone has experienced trying, but failing to master a difficult book that was begun with the hope of increasing one's understanding. When that happens, it is 36 to think that it was a mistake to try to read it, but that was not the mistake. The mistake was in 37 too much from the first reading of a(n) 38  book. If you read it in the right way, no book written for the 39 reader, no matter how difficult, need be a cause for despair(令人失望).

What is the right method? The 40 is an important and helpful rule of reading that is either not  41  or often forgotten. That rule is simply this: when reading a difficult book for the first time, read it through without ever  42  to think about the things that you do not understand immediately.

Do not be stopped by what you  43  understand. Read through the difficult  44 ,and you soon come to things that you do understand. Read these  45 .You will have a much better chance of understanding all of the book when you read it again, but that  46  you to have read the book through once  47 .

What you understand by reading the book through to the 48  will help you when you try later to read the places that you did not  49  in your first reading. Or if you never re-read the book, understanding half of it is much better than understanding  50  of it, which will happen  51  you allow yourself to be stopped by the first difficult part of the book.

Most of us were taught to  52  the things that we do not understand. We were told to find the  53  of unfamiliar words, and to try to find an explanation in another  54  for anything that we did not understand in the book that we were reading. But when these things are done before the proper time, they only  55 our reading, instead of helping it.

36. A. necessary     B. useful C. natural       D. effective

37. A. learning       B. wanting      C. accepting    D. expecting

38. A. easy     B. difficult     C. important   D. correct

39. A. ordinary      B. young C. serious       D. sincere

40. A. method B. question     C. answer       D. problem

41. A. taught   B. known       C. sure    D. perfect

42. A. starting B. hesitating   C. Stopping    D. repeating

43. A. can't     B. won't  C. mustn't       D. wouldn't

44. A. words   B. articles       C. parts   D. points

45. A. quickly B. immediately      C. clearly       D. carefully

46. A. requires       B. causes C. advises       D. allows

47. A. later     B. after   C. before D. again

48. A. top       B. end     C. bottom       D. cover

49. A. see       B. turn    C. Notice D. understand

50. A. anything      B. everything  C. nothing      D. something

51. A. if B. so that  C. whenever   D. as though

52. A. put away      B. put down    C. think of      D. think about

53. A. uses      B. Meanings   C. Spellings    D. troubles

54. A. thinking       B. reading      C. Book  D. way

55. A. harm    B. increase      C. Improve     D. prevent

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