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问题 计算题

(11分)光滑水平面上放有如图所示的用绝缘材料制成的“┙”型滑板（平面部分足够长），滑板的质量为4m。距离滑板的右壁A为L1的B处放有一质量为m、电量为+q(q>0)的小物体（可视为质点），小物体与板面之间的摩擦可忽略不计。整个装置处于场强为E、方向水平向右的匀强电场中。开始时，滑板与小物体都处于静止状态，某时刻释放小物体，求：

（1）小物体第一次跟滑板的A壁碰撞前瞬间的速度v1多大;

（2）若小物体与A壁碰撞时间极短，且碰撞过程没有机械能损失，则

a.小物体第二次即将跟A壁碰撞瞬间，滑板的速度v和小物体的速度v2分别为多大;

b.从开始释放小物体到它即将第二次跟A壁碰撞的过程中，整个装置的电势能减少了多少.

答案

（1）（2）a.;b:

题目分析：由动能定理得：           1分

得               1分

（2）a．小物体与A壁碰撞时间极短，且碰撞过程没有机械能损失

由动量守恒得             1分

机械能守恒             1分

可得               1分

设再经过t发生第二次碰撞，则             1分

可得              1分

               1分

b.小物块跟A壁第一次碰撞后到即将第二次跟A壁碰撞的过程中，滑板的位移             1分

小物体从释放到即将第二次跟A壁碰撞过程中

电场力对它所做的功：        1分

所以整个装置的电势能减少量ΔE=W=         1分

单项选择题

现在的马拉松赛跑是为了纪念（）中为报信而死的勇士。

A、希波战争

B、伯罗奔尼撒战争

C、斯巴达波斯战争

D、希腊土耳其战争
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单项选择题

Anthropology is the study of human beings as creatures of society. It (1) its attention upon those. physical characteristics and industrial techniques, those conventions and values, which (2) one community from all others that belong to a different tradition.

The distinguishing mark of anthropology among the social sciences is that it includes for serious study other societies (3) our own. For its purposes any social (4) of mating and reproduction is as significant as our own. To the anthropologist our customs and those of a New Guinea tribe are two possible social schemes for (5) a common problem, and in so far as he remains an anthropologist he is (6) to avoid any weighting of one (7) the other. He is interested in human behavior, not as it is shaped by one tradition, our own, but as it has been shaped by any tradition (8) He is interested in a wide (9) of custom that is found in various cultures, and his object is to understand the way in which these cultures change and (10) , the different forms through which they express themselves and the (11) in which the customs of any peoples function in the lives of the (12) .

Now custom has not been commonly regarded as a (13) of any great moment. The inner workings of our own brains we feel to be uniquely (14) of investigation, but custom, we have a way of thinking, is behavior at its most commonplace. (15) , it is the other way round. Traditional custom is a mass of detailed behavior more astonishing than (16) any one person can ever evolve in individual actions. Yet that is a rather (17) aspect of the matter. The fact (18) first rate importance is the predominant role that custom (19) in experience and belief, and the very great varieties it may (20)

7（）

A. in favor of

B. instead of

C. rather than

D. in contrast with
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