问题 选择题

如图所示,半径R=0.4m的光滑半圆环轨道处于竖直平面内,半圆环与粗糙的水平地面相切于圆环的端点A 且μ=0.4。一质量m=0.1kg的小球,以初速度v0=8m/s在粗糙水平地面上向左作直线运动,运动4m后,冲上竖直半圆环,经过最高点B后飞出。取重力加速度g=10m/s2。求:

(1)小球到达A点时速度大小;

(2)小球经过B点时对轨道的压力大小;

答案

(1) (2)3N

题目分析:(1)小球从开始运动到到达A点的过程中,由动能定理

代入数据解得 

(2)由A点到B点由机械能守恒定律得

在B点时根据牛顿定律

联立上述两式可解得   

完形填空

 完形填空(共20小题;每小题1.5分,满分30分)

阅读下面短文,掌握其大意,然后从36—55各题所给的四个选项(A、B、C和D)中,选出最佳选项,并在答题卡上将该项涂黑。

Attracting People to You

In West Virginia folklore there is a story of a country doctor. He was   36   late one night to    assist a woman who was about to give birth. By the time the doctor arrived at the farmhouse, things had   37   to a point where the doctor asked the husband to help him by holding a gas lantern up high in order to   38   the room.

Before long, the   39   mother delivered a healthy baby boy. As the father   40   the lantern, the doctor shouted an   41   to keep the lantern high: “We’re not done yet.”   42  , a second child appeared on the   43  , a healthy baby girl. Shaken by the unexpected arrival of twins, the father heard the doctor say once again, “We can’t   44   now. It looks as if it’s going to be triplets (三胞胎).” To which the   45   father, still holding the lantern high, replied, “Do you think it’s the light that’s   46   them?”

Light has a quality of attraction. I recently left my office door   47   late one afternoon in our mountain home and, at dusk, the   48   from within attracted a bird!

You, too, have a light that attracts … an inner light. Not   49   to the naked eye (肉眼), but obvious just the same. Some people   50   with a light of kindness. Others emit (散发,发射) a light of hope.

Almost all   51   are drawn to light, including humans. Do you want to attract people to you?   52   inner qualities can attract people like a warm fire on a   53   night. What will draw other people to you best cannot be   54   in any department store.

You may not always see it,   55   your light is shining through. And it’s one of your most attractive qualities!

36. A. called out     B. called on    C. called off   D. called back

37. A. happened     B. gone   C. turned D. progressed

38. A. decorate       B. darken       C. light   D. show

39. A. adventurous B. brave  C. humorous   D. dangerous

40. A. lowered       B. raised  C. weakened   D. brightened

41. A. order    B. idea    C. apology      D. excuse

42. A. Strangely     B. Shortly      C. Gradually   D. Lately

43. A. air B. screen C. scene  D. way

44. A. continue      B. help    C. argue  D. stop

45. A. worried       B. amazed      C. puzzled      D. amused

46. A. attracting     B. interesting  C. pulling       D. introducing

47. A. shut      B. locked C. open   D. wide

48. A. food     B. water  C. sound  D. light

49. A. comfortable B. visible C. available    D. valuable

50. A. shine    B. work   C. live     D. provide

51. A. creatures      B. birds   C. animals      D. plants

52.。A. Negative B. High   C. Positive      D. Poor

53. A. windy   B. cold    C. rainy   D. dark

54. A. exhibited     B. changed     C. exchanged  D. purchased

55. A. because B. since   C. but     D. if

单项选择题