如图所示，光滑曲面AB与水平面BC平滑连接于B点，BC右端连接内壁光滑、半径为r的细圆管CD，管口D端正下方直立一根劲度系数为k的轻弹簧，轻弹簧一端固定，另一端恰好与管口D端齐平。质量为m的小球在曲面上距BC的高度为2r处从静止开始下滑，小球与BC间的动摩擦因数μ=，进入管口C端时与圆管恰好无作用力，通过CD后压缩弹簧，在压缩弹簧过程中速度最大时弹簧的弹性势能为EP。求
（1）小球达到B点时的速度大小vB；
（2）水平面BC的长度s；
（3）在压缩弹簧过程中小球的最大速度vm 。
（1）
（2）s=3r（3）
题目分析：（1）由机械能守恒得
（2分）
得（1分）
（2）由
（2分）
得vC= 
（1分）
由动能定理得
（3分）
解得s=3r（2分）
（3）设在压缩弹簧过程中速度最大时小球离D端的距离为x，则有kx=mg （2分）
得
（1分）
由功能关系得
（3分）
得
| 阅读理解。 | |||||
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| 1. On Saturday morning, you can _____. | |||||
[ ] | |||||
| A. go to watch a ball game B. take children to play games at the City Theatre C. go to the Central Park for a picnic | |||||
| 2. The Red Birds ballgame _____. | |||||
[ ] | |||||
| A. is in the afternoon B. is outside C. is at the gate | |||||
| 3. You can eat many different food from all over the world if you _____. | |||||
[ ] | |||||
| A. go to the City Theatre B. go to the Central Park C. buy tickets at the gate | |||||
| 4. "The Zoo" is _____. | |||||
[ ] | |||||
| A. a US concert B. a park with many red birds in it C. a music group | |||||
| 5. Mr. Turner wants to have a nice Saturday. Which is not possible for him to do? | |||||
[ ] | |||||
| A. Watching a ballgame and having a picnic. B. Having a picnic and seeing a film. C. Listening to a concert and watching a ballgame. |