3、如图所示，在竖直平面内固定着光滑的1/4圆弧槽，它的末端水平，上端离地高H。一个小球从上端无初速度滑下，若要小球的水平射程为最大值，则圆弧槽的半径为_______，最大的水平射程为_________。

2．如图所示，水平粗糙地面上的物体被绕过光滑定滑轮的轻绳系着，现以大小恒定的拉力F拉绳的另一端，使物体从A点起由静止开始运动。若从A点运动至B点和从B点运动至C点的过程中拉力F做的功分别为W₁、W₂，若图中AB=BC，且动摩擦因数处处相同，则在物体的运动过程中，物体对地面的摩擦力______________(选填“增大”、“不变”或“减小”)，W₁_________W₂(选填“＜”、“＝”或“＞”)。

1．把小球水平抛出，空气阻力不计，抛出后在t₁、t₂两个时刻，小球的速度与水平方向的夹角分别是30º、45º，则t₁：t₂=　　　　　　 　　　，小球自抛出到此两个时刻下落的高度之比h₁：h₂=　　　　　　 。

10.(　　 ) Although he had taken a lot of medicine, his health ____ poor. (NMET 2002 上海春招)

　　　　　　 A. proves　　　　　　 B. remains

　　　　　　 C. maintains　　　　　 D. continues

　　 [解析]选B remain表示“依然，还是”，是系动词，后接形容词作表语，符合句意。

9. -- Are you still thinking about yesterday' s game?

　　　 -- Oh, that' s __　 (NMET 2003 北京春招)

　A. what makes me feel excited

　B. whatever I feel excited about

C. how I feel about it

D. when I feel excited

　　 [解析]选A　 根据句意，排除B、C。D项句意符合，但时态不正确。

8. Not a single song ____ at yesterday’s party.(2000 上海)

A. she sang　　　　　 B. sang she

C. did she sing　　　　 D. she did sing

　　 [解析]选C　 否定词not在前，句子要倒装且要用部分倒装。

7. Johnson ____ his wife and ____ smoking. (NMET 2002)

　　 A. gave up; gave in

　　 B. gave away to; gave up

　　 C. gave in to; gave up

　　 D. gave away to; gave out

　　 [解析]选C　 本题考查四个短语的区别：give up “放弃”；give in to “向……让步”；give away to “背弃，出卖，泄密”；give out “耗尽，用光”。

6.(　　 ) Lisa ____ a book in Chinese last year, but I don't know whether she has finished it.

　　 A. wrote　　 B.　 has written

　　　 C. was writing　　 D. had written

　　 [解析]选C　 but I don't know whether she has finished it，暗示过去的动作仍在进行，过去进行时可表示过去某个时期阶段性的动作或状态。

5．(　　 )I really can' t understand ____ her like that. (2005安徽)

　　 A. you treat　　 B. you to treat

　　 C. why treat　　 D. you treating

　　 [解析]选D understand后可接从句，名词或u-ing形式等，故选D。若选A，选项须改为why you treat。

4. I don' t think I'll need any money but I'll bring some ____. (NMET 2000)

　　　　　　 A. at last　　　　　　　 B. in case

　　　　　　 C. one again　　　　 D. in time

　　 [解析]选B　　 A、B、C、D四个短语意义各不相同，A“最后”；C“再一次”；D“及时”；B“以防；万一”。从句意来看，应选in case，因为句子暗示“带一些钱以防(备用)”之意，相当于：I’ll bring some in case I need money．