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问题 问答题

如图11-4-4所示，光滑的半球壳半径为R,O点在球心的正下方，一小球由距O点很近的A点由静止放开，同时在O点正上方有一小球自由落下，若运动中阻力不计，为使两球在O点相碰，小球由多高处自由落下（＜＜）.

图11-4-4

答案

(n=1,2,3，…)

小球由A点由静止释放运动到O点的时间为（2n-1）,n=1,2,3，…，由于O点正上方自由落下的小球到O的时间也为(2n-1)时两球才能在O点相碰，所以

h=gt2=g(2n-1)2=(n=1,2,3，…)

选择题

目前，在我国600个城市中，有400多个城市供水不足，其中最缺水的城市有110个，城市缺水总量达到60亿立方米。水利部（（21世纪中国水供求》预测2010年后，我国将开始进入严重缺水期，至2030年，我国将出现缺水高峰。材料说明

①我国正面临水资源危机

②水资源短缺将危及人类生存和发展

③必须实施可持续发展战略

④把保护水资源作为我党工作的中心

A．①②③

B．①②④

C．①③④

D．②③④
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单项选择题

Some of the concerns surrounding Turkey’s application to join the European Union, to be (1) on by the EU’s Council of Ministers on December 17th, are economic--in particular, the country’s relative poverty. Its GDP per head is less than a third of the average for the 15 pre-2004 members of the EU. (2) it is not far off that of Latvia--one of the ten new members which (3) on May 1st 2004, and it is much the same as (4) of two countries, Bulgaria and Romania, which this week concluded (5) talks with the EU that could make them full members on January 1st 2007.

(6) , the country’s recent economic progress has been, according to Donald Johnston, the secretary-general of the OECD, stunning. GDP in the second quarter of the year was 13.4% higher than a year earlier, a (7) of growth that no EU country comes close to (8) . Turkey’s (9) rate has just fallen into single figures for the first time since 1972, and this week the country (10) agreement with the IMF on a new three-year, $10 billion economic program that will help Turkey (11) inflation toward European levels, and enhance the economy’s resilience.

Resilience has not historically been the country’s economic p point. (12) , throughout the 1990s growth oscillated like an electrocardiogram (13) a violent heart attack. This (14) has been one of the main reasons why the country has failed dismally to attract much-needed foreign direct investment. Its stock of such investment is lower now than it was in the 1980s, and annual (15) have scarcely ever reached $1 billion.

One deterrent to foreign investors is due to (16) on January 1st 2005. On that day, Turkey will take away the right of virtually every one of its citizens to call themselves a millionaire. Six zeros will be removed from the face value of the lira (里拉，土耳其货币单位); one unit of the local (17) will henceforth be worth what 1 million are now--ie, about ￡ 0.53 (0.53 欧元). Goods will have to be (18) in both the new and old lira for the whole of the year, (19) foreign bankers and (20) can begin to look forward to a time in Turkey when they will no longer have to juggle mentally with indeterminate strings of zeros.

19（）

A.though

B.but

C.for

D.since
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