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质量为m=20kg的物体，在大小恒定的水平外力F作用下，沿水平面做直线运动．在0～2s内F与运动方向相反，在2～4s内F与运动方向相同．该物体的v-t图象如图所示．取g=10m/s2，求物体与水平面间的动摩擦因数μ．

答案

由图象可得：0～2s内物体做匀减速直线运动，加速度大小为：a1=5 m/s2，2s～4s内物体做匀加速直线运动，加速度大小为：a2=1m/s2，根据牛顿第二定律得：

             F+Ff=ma1

             F-Ff=ma2

             又Ff=μmg，

解得：μ=0.2

答：物体与水平面间的动摩擦因数为0.2

单项选择题

政策的执行机关既有组织的一般性和独具的特性，又具有政策执行者所赋予的特性，具体而言，以下哪项不是它所具有的特性（）。

A.执行性

B.服务性

C.创新性

D.法制性
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填空题

According to historical records，the first (1) Olympic Games can be traced back to 776 BC.They (2) dedicated to the Olympian gods and were staged on the (3) plains of Olympia.They continued for nearly 12 centuries， (4) Emperor Theodosius decreed in 393 A.D.that aU such"pagan cults" (5) banned.
The oldest myth which concerns the beginning of the (6) Games is that of Idaios Daktylos Herakles.According to other (7) ，Zeus，the father of humanity，fought and defeated Cronus in a (8) for the throne of the gods.Finally，the well-known (9) Herakles is mentioned who staged games in Olympia in honour (10) Zeus,because the latter had helped him conquer Elis when (11) went to war against Augeas.
Through the 12 centuries of (12) Olympic Games，many wonderful athletes competed in the stadium and (13) hippodrome of ancient Olympia’s sacred area，moving the crowds with (14) great achievements.Although mortal，their Olympic victories immortalised them.Of (15) best athletes who left their mark on the sacred vallev (16) Olympia，some surpassed all limits and became legends by winning (17) successive Olympic Games and remaining at the forefront of their (18) for more than a decade.
The ancient Olympic Games were (19) a one.day event until 684 BC.when they were extended (20) three days.In the 5th century B.C.，the Games were extended again to cover five days.
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