问题 计算题

轻绳AB总长l,用轻滑轮悬挂重G的物体。绳能承受的最大拉力是2G,将A端固定,将B端缓慢向右移动d而使绳不断,求d的最大可能值

答案

以与滑轮接触的那一小段绳子为研究对象,在任何一个平衡位置都在滑轮对它的压力(大小为G)和绳的拉力F1、F2共同作用下静止。而同一根绳子上的拉力大小F1、F2总是相等的,它们的合力N是压力G的平衡力,方向竖直向上。因此以F1、F2为分力做力的合成的平行四边形一定是菱形。利用菱形对角线互相垂直平分的性质,结合相似形知识可得d∶l =∶4,所以d最大为

判断题
单项选择题

With the spread of inter-active electronic media a man alone in his own home will never have been so well placed to fill the inexplicable mental space between cradle and crematorium. So I suspect that books will be pushed more and more into those moments of travel or difficult defecation (1) people still don’t quite know what to do with.

When people do read, I think they’ll want to feel they are reading literature, or (2) something serious. (3) you’re going to find fewer books presenting themselves as no- nonsense and (4) assuming literary pretensions and being packaged as works of art. We can expect an extraordinary variety of genre, but with an underlying (5) of sentiment and vision.

Translators can only (6) from this desire for the presumably sophisticated. We can look forward to lots of difficult names and fantastic stories of foreign parts enthusiastically (7) by the overall worship of the "global village" Much of this will be awful and some wonderful, (8) don’t expect the press or the organizers of prizes to offer you much help in making the appropriate distinctions. They will be chiefly (9) in creating celebrity, the greatest enemy of discrimination, but a good prop for the (10) consumer.

Every ethnic grouping over the world will have to be seen to have a great writer--a phenomenon that will (11) a new kind of provincialism, more chronological than geographic, (12) only the strictly contemporary is talked about and (13) . Universities, including Cambridge, will include (14) their literature syllabus novels written only last year. (15) occasional exhumation for the Nobel, the achievements of ten or only five years ago will be largely forgotten.

In short, you can’t go too far wrong when predicting more of the same. But there is a (16) side to this--the inevitable reaction against it. The practical things I would like to see happen--publishers seeking less to (17) celebrity through extravagant advertising, (18) and magazines (19) space to reflective pieces--are rather more improbable than the Second Coming (耶稣复临). But dullness never quite darkens the whole planet. In their own idiosyncratic fashion a few writers will (20) be looking for new departures.

17()

A.prevent

B.explore

C.prohibit

D.generate