试题与答案

如图所示,质量为M的木板长为L,木板的两个端点分别为A、B,中点为O,木板置于光

题型:计算题

题目:

如图所示,质量为M的木板长为L,木板的两个端点分别为A、B,中点为O,木板置于光滑的水平面上并以v0的水平初速度向右运动。若把质量为m的小木块(可视为质点)置于木板的B端,小木块的初速度为零,最终小木块随木板一起运动。小木块与木板间的动摩擦因数为μ,重力加速度为g。求:

(1)小木块与木板相对静止时,木板运动的速度;

(2)从小木块放上木板到它与木板相对静止的过程中,木板运动的位移;

(3)小木块与木板间的动摩擦因数μ的取值在什么范围内,才能使木块最终相对于木板静止时位于OA之间。

答案:

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参考答案:C解析: 索引按功能分为普通索引、唯一索引、候选索引和主索引。索引除了具有建立记录逻辑顺序的作用外,还能控制是否允许相同的索引关键字值在不同记录中重复出现,或允许在永久关系中建立参照完整性...

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Among the major values of the modern period, four typically manifest themselves in the cultural environment: celebrating the individual, believing in rational order, working efficiently, and rejecting tradition. These values of the modern period were originally embodied in the printing press and later in newspapers and magazines. The print media encouraged the vision of individual writers, publishers, and readers who circulated new ideas. Whereas the premodern period was guided by p beliefs in a natural or divine order, becoming modern meant elevating individual self-expression to a central position. Along with democratic breakthroughs, however, individualism and the Industrial Revolution triggered modern forms of hierarchy, in which certain individuals and groups achieved higher standing in the social order. For example, those who managed commercial enterprises gained more control over the economic ladder, while an intellectual class of modern experts, who mastered specialized realms of knowledge, gained increasing power over the nation’s social, political, and cultural agendas.

To be modern also meant to value the capacity of organized, scientific minds to solve problems efficiently. Progressive thinkers maintained that the printing press, the telegraph, and the railroad in combination with a scientific attitude would foster a new type of informed society. At the core of this society, the printed mass media, particularly newspapers, would educate the citizenry, helping to build and maintain an organized social framework. Journalists strove for the premodern ideal through a more fact-based and efficient approach to reporting. They discarded decorative writing and championed a lean look. Modern front-page news de-emphasized description, commentary, and historical context. The lead sentences that reported a presidential press conference began to look similar, whether they were on the front page in Tupelo, Mississippi, or Wahpeton, North Dakota. Just as modern architecture made many American skylines look alike, the front pages of newspapers began to resemble one another.

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