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问题 计算题

如图所示，质量分别为mA和mB的A和B两球用轻弹簧连接，A球用细线悬挂起来，两球均处于静止状态.如果将悬挂A球的细线剪断，此时A和B两球的瞬间加速度各是多少？

答案

解：物体在某一瞬间的加速度，由这一时刻的合外力决定，分析绳断瞬间两球的受力情况是关键。由于轻弹簧两端连着物体，物体要发生一段位移，需要一定的时间，故剪断细线瞬间，弹力与断前相同

先分析平衡（细线未剪断）时，A和B的受力情况如图所示，A球受重力、弹簧弹力F1及绳子拉力F2且mAg+F1=F2；B球受重力、弹力F1'，且F1'=mBg

剪断细线瞬间，F2消失，但弹簧尚未收缩，仍保持原来的形变，F1不变，故B球所受的力不变，此时aB=0，而A球的加速度为：，方向竖直向下

单项选择题

German Chancellor Angela Merkel won over German voters in the Federal Election on Sept. 27. Can she now be won over by a French charm offensive (1) at repairing the relationship that was once at the heart of Europe That’s the question being asked in Paris, (2) top government officials are (3) talking about their desire to rekindle closer ties (4) their neighbors across the Rhine. (5) the end of World War II the Franco-German relationship has been the motor of European integration, the (6) force behind the creation of the European Union and, more recently, the introduction of the euro. But the ardor has (7) in this decade, particularly under Merkel, who has regularly struggled to (8) her irritation with French President Nicolas Sarkozy’s grandstanding. Sarkozy, (9) , has often been impatient with what he (10) Merkel’s lack of resolve.

The sometimes (11) personal rapport is a long way from the public shows of affection their predecessors staged, particularly Helmut Kohl and FranCois Mitterrand, who movingly held (12) in 1984 in a Verdun cemetery. There’s been tension on (13) , too. Charles Grant, director of the London-based think tank Centre for European Reform, points out that France and Germany have been (14) on issues from how best to reflate their economies during the economic (15) to the smartest strategies for dealing with Russia.

But influential movers in France are now (16) to put the relationship back on a friendlier footing. In a recent paper French think tank Institute Montaigne (17) an ambitious agenda for the two nations, (18) that a new impetus is needed if Europe’s voice is to be heard in a world (19) of big new players, such as Brazil and India, and at a time when President Obama seems fax more (20) with China and the rest of Asia than with America’s traditional allies in Europe.

17（）

A. turned out

B. laid out

C. made out

D. gave out
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单项选择题

中国人民银行发布的《2013年第3季度储户问卷调查报告》显示：倾向于储蓄和消费的居民占比均有所下降，而倾向于“更多地去投资”的人数则有所增加。造成这一现象的原因可能有（）

①城乡居民的可支配收入减少

②人们投资理财的意识在不断增强

③存款利率偏低，消费价格指数（CPI）偏高

④投资能够获得稳定的高收益

A.①②

B.①④

C.②③

D.②④
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