题目

如图所示，在动摩擦因数为μ的水平面上有A、B两个质量均为m的滑块，用劲度系数为k的轻质弹簧相连，弹簧始终在弹性限度内，现有一与水平面成45°角的力F作用在滑块B上，A、B刚好不滑动，设最大静摩擦力等于滑动摩擦力，则拉力F的大小为（ ）A. B. C. D. 答案：【答案】C【解析】A、B刚好不滑动，AB与水平面恰好达到最大静摩擦力，分别隔离A和B受力分析由平衡条件列式求解即可。A、B刚好不滑动，AB与水平面恰好达到最大静摩擦力，隔离A受力分析由平衡条件得：F弹＝μmg，隔离B受力分析由平衡条件得：Fcos45°＝F弹+μ（mg﹣Fsin45°），联立解得：，故ABD错误，C       As darkness fell, hundreds of people in the Swiss village left their houses. They were staring  36  at the mountain top in the distance. It was covered with ice and snow beautiful and  37 .        The huge mountain is called Matterhorn. The mountain climbers had  38  the top，using the southern route（路线）. But no one had ever  39  to try a winter climbing up the northern side. But now one man was daring to try the  40  route. He was Walter Bonatti, a great mountain climber from Italy.        For two days he had climbed. The village people had  41  him anxiously. Now they were waiting to see his  42  . If he planned to  43  the next day，he would light a green signal. A red light would mean that he was turning.        A tiny green light  44  high on the mountain side. Bonatti was not giving up！The people  45  .        The next day he  46  his way upward. He was so lonely and so  47 ！But he would not give up. Again that night he lit the  48  light.        In the morning, Bonatti  49  up. He could not see the top，but he knew he was  50  there. Though the climb was painful，he moved up.        Bonatti had spent months  51  for the climb. Was the training enough?  Did he have the strength and  52  to climb to the top?         He was  53  at the top！News about his victory（胜利） was radioed to the world.        The trip  54  the southern route was easy. He was warmly welcomed in the village. He had done the  “ 55 ,” and would be well remembered as a climber forever. 36. A. eastwardB. forwardC. downD. up 37. A. specialB. dangerousC. attractiveD. obvious 38. A. borderedB. passedC. reachedD. climbed 39. A. permittedB. admiredC. thoughtD. dared 40. A. difficultB. novel C. sameD. easy 41. A. surroundedB. terrifiedC. watched D. helped 42. A. faceB. figureC. flagD. signal 43. A. settle down B. go onC. give upD. throw away44. A. appearedB. showedC. disappearedD. hung45. A. laughedB. cheeredC. jumpedD. shouted46. A. continuedB. started C. stoppedD. led47. A. sleepyB. excitedC. tiredD. happy 48. A. yellowB. blueC. greenD. red 49. A. wokeB. turnedC. gotD. looked 50. A. alreadyB. almostC. extremelyD. surely 51. A. trainingB. accountingC. planningD. asking 52. A. courageB. skillC. moneyD. wish 53. A. finallyB. graduallyC. officiallyD. slightly 54. A. alongB. upC. downD. to 55. A. necessaryB. importantC. limitedD. impossible