问题 选择题

如图所示,OA为一质量分布均匀的横梁,横梁始终保持水平状态,被一轻质钢索AB拉着,O为无摩擦铰链,重物在水平恒力F作用下从O点出发向右作匀加速直线运动,钢索中的拉力为T,物体到O点的距离为X,物体运动的时间为t,则下图中能正确描述T-X、T-t之间关系的是(  )

A.

B.

C.

D.

答案

设OA杆长为L,重力为G1,重物的重力为G2

对杆OA研究,以O转轴,由力矩平衡条件,得

    TLsinA=G1

1
2
L+G2X

得到T=

G2
sinA
X+
G1
2sinA
,T-X图象是不过原点的倾斜直线.

由题X=

1
2
at2,代入得T=
G2a
2sinA
t2+
G1
2sinA
,当t=0时,T>0,是开口向上的抛物线.故A正确.

故选A.

单项选择题 B型题
完形填空

三、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、D四个选项中,选出最佳选项。

My friend Jessie and I have known each other since we were very young. After we both got married we seldom had time to get together    36    I always promised myself that I would meet her whenever I was free.

Friendships get more    37    as we get older. When we reached our forties, we    38    to do something to keep our    39    strong, healthy and growing. We picked out one Saturday a month and    40    to do something together that day. Sometimes we had a long lunch out, and other times we went to see a movie or went shopping. We also promised to have a(n)    41    every few days.

In some adventures we drove to our favorite places and    42    a night there. Other times we just    43  , stopping wherever we wanted. One of our adventures    44    us to a very small town in south Georgia. The people there were    45    a special festival. We were    46    to buy the handmade gifts and eating the   47    food. There was also a parade. Everyone in the parade    48    and waved to us! It was so great! We    49      had a great time that day!

Fun is always on the menu, whether it’s a weekend trip or a couple of hours    50    lunch. We are so happy and have a great    51    on each other’s lives. We share our sorrow and    52    and we ask for and receive advice. We always laugh, too!

Don’t keep promising yourself that “someday” you’ll    53    your friends. Do it now. Pick up your phone and make a    54    for THIS weekend. You’ll be a happier,    55    person for it! You need it and your friends need it, too.

36. A. as                   B. unless                         C. though                        D. since

37. A. precious              B. difficult                          C. boring                  D. interesting

38. A. refused           B. decided                           C. remembered             D. regretted

39. A. friendship           B. connection                   C. marriage                  D. life

40. A. forgot                 B. promised                         C. learned                     D. pretended

41. A. racing                 B. adventure                        C. hiking                  D. appointment

42. A. offered           B. took                                C. cost                         D. spent

43. A. looked            B. left                                 C. drove                       D. ran

44. A. gave                   B. took                                C. pushed                     D. forced

45. A. obtaining            B. enjoying                          C. preparing                 D. representing

46. A. unwilling            B. eager                              C. delighted                  D. neat

47. A. delicious             B. terrible                            C. awful                       D. valuable

48. A. wiped                 B. appealed                          C. smiled                  D. announced

49. A. hardly                B. nearly                         C. really                       D. probably

50. A. over                   B. on                                  C. at                               D. with

51. A. regret                 B. influence                         C. discussion             D. impression

52. A. weakness            B. benefits                           C. problems                  D. happiness

53. A. meet                   B. advise                         C. support                    D. grasp

54. A. design            B. plan                                C. speech                  D. record

55. A. busier                 B. prettier                            C. healthier                   D. cleaner