高台滑雪运动员腾空跃下，如果不考虑空气阻力，则下落过程中该运

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问题选择题

高台滑雪运动员腾空跃下，如果不考虑空气阻力，则下落过程中该运动员机械能的转换关系是

A．动能减少，重力势能减少

B．动能减少，重力势能增加

C．动能增加，重力势能减少

D．动能增加，重力势能增加

答案

答案：C

滑雪运动员跃下过程中，重力做正功，重力势能减小，动能增加，C对，ABD错。

填空题

根据句意，选择适当的词语填空。

1. Someone will probably find it and _______ (return, return to) it sooner or later.

2. She was ________ (worried about, worried) and asked him if he had seen a history book.

3. It looks ________ (exciting, excited), but I don't know how to surf.

4. Hawaii is famous ________ (for, of) its beautiful beaches.

5. His teacher, Miss Lee, spoke ________ (highly, high) of her student.

6. There was a truck _______ (collecting, collects) rubbish and throw it in.

7. You have helped _______ (protect, product) our environment.

8. There is _______ (much too, too much) water here. How can I get past?

9. Don't forget ________ (to tell, telling) me the time. I'd like to join you.

10.Make sure that all of the rubbish _______ (go, goes) into the dustbin.

计算题

如图所示，AB是倾角为的粗糙直轨道，BECD是圆心为O的光滑圆轨道，半径为R，与AB在B点相切. 一质量为m质点，从直轨道上P点由静止释放，P、O、C三点在同一水平直线上，E为最低点，质点与AB直轨道动摩擦因数为，重力加速度为g，求：

（1）质点第一次通过E点向左运动时轨道对其支持力大小；

（2）质点在AB直轨道上运动的最大路程（质点没有脱离原轨道）；

（3）为了不脱离轨道在轨道上往复运动，则释放点改为点，则点离B的点距离最大不超过多少？