问题 计算题

(10分)如图所示,竖直平面内的光滑弧形轨道的底端恰好与光滑水平面相切。质量为M=2.0kg的小物块B静止在水平面上。质量为m=1.0kg的小物块A从距离水平面高h=0.45m的P点沿轨道从静止开始下滑,经过弧形轨道的最低点Q滑上水平面与B相碰,碰后两个物体以共同速度运动。取重力加速度g=10m/s2。求

(1)A经过Q点时速度的大小v0

(2)碰撞过程中系统(AB)损失的机械能ΔE.

答案

(1)3.0m/s

(2)3.0J

(1)AP滑到Q的过程中,根据机械能守恒定律得

                        ( 2分)

解得A经过Q点时速度的大小             (2分)

(2)AB相碰,根据动量守恒定律得

mv0=(m + M ) v                       (1分)

解得    .0m/s                   (2分)

根据能量守恒定律得

                  (2分)

解得AB碰撞过程中系统损失的机械能ΔE = 3.0 J                 ( 1分)

多项选择题
完形填空

第二节:完形填空(共20小题;每小题1.5分,满分30分)

阅读下面短文,从短文后所给各题的四个选项(A、B、C和D)中,选出可以填入空白处的最佳选项。

When my son was 11 years old, he got a small job helping out with a traveling carnival in our town. He didn't come home at lunch time, phoning  36  to tell me he was fine and had found a few days' work  37  out at an exhibit. However, after he finished work he  38  for supper as usual.

I asked him how he had  39  at lunch and he told me he had made some new  40  at the carnival, some young men who were twin brothers, and their mom and dad. They had  41  him a few dollars and invited him for lunch  42  for helping them set up their exhibit and wanted him to  43   the next day to help with other chores (杂务).

I was glad he had found new friends but a little  44  about the type of people who might be traveling in a carnival. "Oh, Mum, these are just  45  everyday people like anyone else. They  46   work at a carnival instead of in a store or something". "Come down tomorrow and  47  them yourself," he said.

So the next day I went to the carnival and to the exhibit he had  48  me to. The twin brothers   _49  out to be Siamese (连体的) twins, joined at the chest. He hadn't thought this  50  was noteworthy enough to mention. When I brought it to him, he said, "yes, I  51  that too. Do you know that their mum has to make all their clothes  52  it's so difficult to find anything to fit them? They're also really good  53  . Today, Joe, one on the fight, made me spaghetti (意大利面条) for lunch. "

What others see first in a person is not what a child considers  54  . Where I saw Siamese twins, he saw people having difficulty buying clothes that fit, and young men who were good cooks. It was a   _55  I have thought about many times over the years.

36. A. instead                B. even              C. also              D. besides

37. A. helping             B. helping                    C. taking             D. showing

38. A. did up                       B. gave up                    C. took up                    D. turned up

39. A. sought                       B. managed                  C. worked                    D. acted

40. A. clothes                       B. friends                            C. choices                     D. differences

41. A. paid                          B. charged                    C. lent                          D. owed

42. A. by chance                  B. in return                   C. by turns                   D. in advance

43. A. return                        B. promise                    C. consider                   D. decide

44. A. excited                      B. regretful                   C. worried                    D. optimistic

45. A. humorous                  B. obvious                    C. particular                 D. normal

46. A. just                           B. never                       C. hardly                      D. always

47. A. teach                         B. meet                        C. affect                       D. join

48. A. ordered                      B. directed                    C. forced                      D. persuaded

49. A. worked                      B. left                          C. came                        D. turned

50. A. expression                  B. change                            C. fact                          D. idea

51. A understood                  B. made                       C. noticed                     D. formed

52. A. before                       B. if                             C. after                        D. because

53. A. cooks                        B. doctors                     C. artists                       D. singers

54. A. necessary                   B. important                 C. impossible                D. unlucky

55. A. lesson                        B. festival                     C. task                         D. match