问题 选择题

下列说法正确的是(       )

A.物体在变力作用下,可以做曲线运动

B.物体所受的合外力不为零时,一定做曲线运动

C.物体做曲线运动时所受的合外力一定是变力

D.做匀速圆周运动的物体处于平衡状态

答案

答案:A

圆周运动中物体受到的是变力,A对;只要力与速度共线,物体就会做直线运动,B错;平抛运动中物体所受合力为恒力,C错;.做匀速圆周运动的物体速度方向时刻发生变化,不是平衡状态,D错。

单项选择题
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.

9()

A. on the whole

B. in turn

C. on the other hand

D. on the contrary