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问题 选择题

如图所示，用细绳拴着质量为m的物体，在竖直平面内做圆周运动，圆周半径为R．，则下列说法正确的是（　　）

A．小球刚好过最高点时的速度是

Rg

B．小球过最高点时的最小速度为零

C．小球过最高点时，绳子张力不可以为零

D．小球过最高点时，绳子对小球的作用力大小不可以等于球所受的重力

答案

A、在最高点的临界情况是拉力T=0，此时有：mg=m

v2
R
，则最小速度v=
gR
．故A正确，B、C错误．

    D、在最高点若速度比较大，拉力和重力的合力提供向心力，有T+mg=m

v2
R
，当T=mg时，v=
2gR
．故D错误．

故选A．

单项选择题

关于工作生活质量的理解不正确的是（）

A、的目标在于提高组织效率，改善雇员工作生活质量

B、工作生活质量对于工作组织来讲是一个过程

C、QWL运动可以用三个D来概括：Development、Dignity和DailyPractice

D、工作生活质量强调企业应该更加追求生产效率
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填空题

The other day my brother Tom was beginning his 56.______
motorbike then our neighbor, Mary came out and asked 57.______
him if he was going near the station. So he offered her a lift.
She got at the back of the motorbike and 58.______
they drove away. Just before they reached to the station 59.______
a policeman waved to them to stop. "Excuse me, sir," he said,
"You are not sitting on that motorbike properly. "
"What’s matter with the way I’m sitting" my brother 60.______
asked in surprise. "Not you sir. It’s a young lady," said 61.______
the policeman, "In this country side-saddle(偏座) is not62.______
permitted when one ride a motorbike．”Mary made an excuse 63．______
that she was from Italy，where it isn’t．considering to 64．______
break the law when people take the side-saddle．
The policeman shook head and drove away． 65.______
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