问题 选择题

如图所示一劲度系数为的轻质弹簧,上端固定,下端连着一质量为m的物块A,A放在托盘B上,初始时全都静止,弹簧处于自然长度,现设法控制B的运动,使A匀加速下降,用表示弹簧伸长量,用表示A的加速度,则在能保持A匀加速下降的整个过程中(始终在弹簧弹性限度内),重力加速度为g,下列说法正确的有 (    )

A.B对A的作用力随弹簧伸长量线性递增

B.若,则弹簧最大形变量为

C.B对A的最大作用力为

D.物块A的重力势能减少了

答案

BD

这个题目是必修一的考查题目。

考查知识点:牛顿第二定律、胡克定律、重力势能

思路分析:先受力分析,利用牛顿第二定律、胡克定律判断A、B、C,再由重力势能公式判断D.

具体解答过程:持A匀加速下降,受力分析,由牛顿第二定律得:mg-F-Kx=ma,则F="mg-ma-kx," B对A的作用力随弹簧伸长量线性递减,A错误

,当弹簧的形变量最大时,F=0,则为,则弹簧的最大形变量为,B正确

当x=0时,F最大为F= mg-ma,C错误

物块A下落的高度为,重力势能减少了,D正确

完形填空

第二节:完形填空(共20小题;每小题1. 5分, 满30分)

“Where is the bus?” I asked myself. I was going to be late and the manager wasn’t going to be pleased. Thank God, here it is! The bus  31  round the corner and I got on. Ten minutes later I was walking into the  32  where I work. “Twenty-five past nine. I 33  the manager doesn’t notice.” But no  34  luck! “Smith!” shouted the manager. “Late again. What’s your 35  this time?”. “ I’m afraid the bus was late, Mr. Brown.” “Get up earlier tomorrow! Anyway, go to your  36  at the counter, we’ll be opening in a few minutes.”

My first customer was a pretty girl wearing a red dress. Behind her was a young man of about 25. He seemed very  37 , and every few seconds he looked  38 the main entrance. The girl  39  about opening a bank account. I gave her the necessary  40  and she walked out. 41 , I noticed a tall man by the door, carrying something  42  with brown paper. Turning to my next customer, I was terrified to see a gun  43  out of his coat. The moment a loud noise  44  my ears. Everything went black. I was falling….

After  45  seemed a very long time, I opened my eyes and found in bed!  46  shaking from the memory of this terrible dream, I got dressed and ran out of the house. As usual, the bus wasn’t on time, and I got to the bank at 9:25.

“Smith!” the manager cried out in a voice like thunder. “  47  of your excuse! Go start work at once!” To my  48 , the first customer was a girl  49  a red dress and behind her stood a man carrying something wrapped in brown paper. The  50 ! Wasn’t that the surprise of my life?

31. A. ran       B. came          C. rode              D. drove

32. A. hotel      B. shop             C. bank              D. restaurant

33. A. believe    B. expect        C. guess             D. hope

34. A. much      B. such           C. more             D. this

35. A. excuse     B. idea            C. cause              D. answer

36. A. business   B. job            C. place           D. spot

37. A. nervous    B. shy             C. calm        D. angry

38. A. down      B. for               C. towards        D. through

39. A. cared      B. talked           C. asked           D. worried

40. A. information  B. offer           C. instruction      D. support

41. A. Again     B. Then           C. Thus           D. However

42. A. hidden     B. rolled          C. filled          D. covered

43. A. getting    B. aiming         C. appearing       D. sticking

44. A. took      B. shook          C. filled          D. covered

45. A. what      B. when           C. that            D. it

46. A. Even            B. Still            C. Just           D. Ever

47. A. Less       B. Plenty         C. More           D. None

48. A. belief     B. surprise        C. joy            D. regret

49. A. of        B. with           C. on             D. in

50. A. dream     B. story           C. affair           D. accident

31—50  BCDBA    CACCA    BDDCA   BDBDA

多项选择题