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问题 选择题

如图所示，一个小球沿竖直固定的光滑圆形轨道的内侧做圆周运动，圆形轨道的半径为R，小球可看作质点，则关于小球的运动情况，下列说法错误的是（　　）

A．小球的线速度方向时刻在变化，但总在圆周切线方向上

B．小球通过最高点的速度可以等于0

C．小球线速度的大小总大于或等于

Rg

D．小球转动一周的过程中，外力做功之和等于0

答案

A、小球的线速度方向时刻改变，沿圆弧的切线方向．故A正确．

B、根据牛顿第二定律，在最高点临界情况是轨道对球的作用力为零，则mg=m

v2
R
．解得v=
gR
．故B错误．

C、最高点的最小速度为

gR
，则小球的线速度的大小总大于或等于
Rg
．故C正确．

D、小球转动一周的过程中，根据动能定理，动能变化为零，则外力做功为零．故D正确．

本题选错误的，故选B．

阅读理解

Sports Club
Sports Club provides you with many different sports to keep healthy. You’ll never get bored. Our programme is always working on new ways to keep you strong and happy. For more information, visit www. mysportsclub.com.
Model Time
If you like models, then Model Time will be the right place for you. From model trains, planes and cars to boats and ships, we have them all! To get more information, please call 885-6321.
Kids Art Club
Kids Art Club gives drawing classes to children aged 7 to 14. Classes are small with only 6 students each. Jim Todd teaches all classes. He has worked in the art field for over 23 years. For more information, please call 885-7621.
Keypals International Club
KIC is a fun club started by kids, for kids aged 8 to 16. KIC tries to help kids understand different cultures through emails and other activities. KIC has members from 40 different countries. For more of it, visit www. worldkids.net.
小题1:If a kid aged 14 wants to know different cultures of the world, he or she can ______.
A．call 885-6321B．visit www. worldkids.net
C．call 885-7621D．visit www. mysportsclub.com
小题2:Which club is organized by kids?
A．Sports Club. B．Model Time.
C．Kids Art Club.D．Keypals International Club.
小题3:If your 8-year-old sister is interested in drawing, she may join ________.
A．Model TimeB．Sports Club
C．Kids Art ClubD．Keypals International Club
小题4:At Kids Art Club, each drawing class has ________ children at most.
A．sixB．sevenC．eightD．fourteen
小题5:Which of the following is TRUE according to the advertisement?
A．Model Time is a good place for us to take a train, plane, boat, etc.
B．We can do different kinds of sports at Sports Club.
C．Keypals International Club is mainly for kids aged 7 to 18.
D．Jim Todd has worked in the art field for less than 23 years.
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多项选择题

以下不属于工程建设其他费中工程保险费的是( )。

A．建筑安装工程一切险

B．施工单位车辆保险

C．进口设备财产保险

D．危险作业意外伤害险

E．人身意外伤害险
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