题目

如图所示，A，B为两个大小可视为质点的小球，A的质量，B的质量，B球用长的轻质细绳吊起，当细绳位于竖直位置，B球处于静止状态时，B球恰好与弧形轨道MN的末端接触但无作用力，已知弧形轨道的内表面光滑，且末端切线水平，现使A球从距轨道末端的高处由静止释放，当A球运动到轨道末端时与B球发生完全弹性碰撞。若取，求：（1）A球刚要接触到B球时的速度大小；（2）两小球相碰撞过程中，B球对A球所做的功；（3）两个小球碰撞后各自开始运动 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，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，选出可以填入空白处的最佳选项。     When I was ten, my family moved to a housing project in East Los Angeles. Even though we struggled to make  36  meet, my parents stressed to me .  37  fortunate we were to live in a great country with  38  opportunities. They imbued(灌输) in me the  39  of family, faith and love for our country.       The following year, my dad, Benjamin, injured his back working in a cardboard-box factory and was  40  as a hairstylist. He rented space in a shopping mall and gave his shop the fancy name of Mr Ben's Coiffure.       The owner of the shopping center gave Dad a discount on his  41  for cleaning the parking lot three nights a week, which  42  getting up at 3 a.m. To pick up trash, Dad used a little machine that looked like a lawn mower  43  Morn and I emptied garbage cans and picked up litter  44  .       I did this job for two years, but the lessons I learned have  45  a lifetime. I acquired discipline, a strong work ethic and a  46  attitude towards life, I also learned at an early age the importance of  47  life's competing interests---in my  48  , school, homework and a job. All  49  helped during my senior year of high school, when I worked 40 hours a week at a fast-food restaurant while  50  precollege courses.       The hard work paid off. I attended the U.S. Military Academy and went on to receive graduate 51  in law and business from Harvard,  52  I joined a big Los Angeles law firm. In these jobs and in everything else I've done, I have never forgotten those days in the parking lot. The experience has  53 me that there is dignity in all work and that if people are working to  54  themselves and their families that is something we should  55  . 36. A. ends         B. demands     C. challenges  D. friends 37. A. so         B. what       C. why        D. how 38. A. priceless      B. resistless     C. limitless     D. sightless 39. A. efforts      B. decisions    C. concepts     D. activities 40. A. retired      B. resigned   C. replaced     D. retrained 41. A. sales         B. rent       C. machine    D. shop 42. A. meant       B. kept        C. needed    D. started 43. A. since        B. although     C. when     D. while 44. A. with joy    B. on purpose C. by hand   D. in time 45. A. proved     B. impressed   C. marked    D. lasted 46. A. practical      B. pleasant      C. positive      D. tolerant 47. A. developing   B. balancing   C. comparing  D. facing 48. A. case       B. example     C. dream     D. attempt 49. A. generally   B. lately      C. really           D. typically 50. A. applying      B. doing      C. following   D. taking 51. A. titles         B. instructions C. chances      D. degrees 52. A. after that      B. ever since  C. after which       D. after then 53. A. equipped      B. prepared   C. taught           D. guided 54. A. serve for      B. feed on    C. provide for       D. count on 55. A. believe     B. honor     C. remember  D. support