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问题 计算题

如图所示，轻杆BC的C点用光滑铰链与墙壁固定，杆的B点通过水平细绳AB使杆与竖直墙壁保持30°的夹角，若在B点悬挂一个质量不计的定滑轮，某人用它匀速地提起重物。已知重物的质量m=30kg，人的质量M=50kg，g=10m/s2。 试求：

（1）此时地面对人支持力的大小；

（2）轻杆BC和绳AB所受力的大小。

答案

解：（1）对重物m由力的平衡条件得：

对人由力的平衡条件得：

而

解得，方向竖直向上

（2）定滑轮对B点的拉力F=2mg，方向竖直向下

杆对B点的弹力方向沿杆的方向，由共点力平衡条件得：

根据牛顿第三定律可得：绳AB所受的力大小为N，杆BC所受的力大小为N

阅读理解与欣赏

读下面唐无名氏的《水调歌》(古代乐曲名)，选出分析不正确的一项

平沙落日大荒西，陇上明星高复低。孤山几处看烽火，壮士连营候鼓鼙。

A．一、二两句写黄昏至星夜军营极目所见。地面辽阔荒远，日落星出，突出了时间的流逝和夜的静谧。

B．第三句陡转，点出军情。幽深的静夜，突然升起几处报警的烽火。“几处”突现了军情的紧急，给人以突兀、危迫之感。

C．第四句写军营的反应。警报传来，战士们迅速 * * 营连成一片，擂响鼓鼙，立即出战迎敌。“鼓鼙”二字突现了将士行动之神速，戒备之森严。

D．全诗以纯客观的笔调写景叙事，采用层层渲染烘托的艺术手法，造成环境气氛上的有张有弛，形成起伏跌宕，读来扣人心弦。
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单项选择题

Questions from 31 to 35 are based on the following passage：Negotiations work wonders ． This is particularly so in international business since it is mostly through negotiations that exporters and importers bridge their differences and reach a fair and mutually satisfactory deal．By presenting a more comprehensive negotiating package in a well planned and organized manner， exporters should be able to improve the effectiveness of their business discussions and in the long term the profitability of their export operations．To avoid being confronted by costly demands ， an exporter should try to determine the buyer’s real interest in the products from the outset． This can be ascertained through appropriate questions but must also be based on research and other preparations before the negotiations．Only then can a suitable counter－proposal be presented．To achieve a favorable outcome from the negotiations， an exporter should draw up a plan of action beforehand， which addresses a few key issues． Experienced negotiators consider that as much as 80% of their overall time devoted to negotiations should go to such preparations． The preliminary work should be aimed at obtaining relevant information on the target market and the buyers of the products． It should also include developing counter－proposals if objections are raised on any of the exporter’s opening negotiating points． The preparations should thus involve formulating the negotiating strategy and tactics．In international marketing negotiations ， it is advisable for small and medium － sized exporters not just to limit their discussions to pricing issues， although pricing is a key factor in any business transaction， exporters should give more attention to the full range of marketing factors． They should stress the strengths of their firms and products and match them with the perceived needs of the buyers． Once these issues have been covered， they can consider the question of price and are able to develop a profitable business．

A successful negotiator should be（ ）.

A．aggressive

B．mild

C．well-prepared

D．hesitative
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