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问题 问答题

一个小行星围绕太阳运行的轨道近似圆形，如果轨道半径是地球轨道半径的9倍，那么该小行星绕太阳运行的周期是多少年？若已知地球绕太阳公转的速度为30km/s，则该小行星绕太阳的公转速度是多少？

答案

太阳对小行星和地球的引力提供它们做圆周运动的向心力．

由G

Mm 
r2 
=m (
2π
T  
)2r 

知：

T1
T2
=
r31
r32
=
93
=27

T1=27年

由G

Mm
r2
=
mv2
r
，v=
GM
r

知：

v1
v2
=
r2
r1
=3

v2=10 km/s

答案：该小行星绕太阳运行的周期是27年，该小行星绕太阳的公转速度是10km/s．

问答题 案例分析题

阅读以下材料，回答问题。

材料一：下图中B区域自16世纪开始欧洲移民大量涌入。目前B区域是世界大城市带之一，钢铁、造船、汽车、飞机制造等工业发达。

材料二：中国是世界最大的钢铁生产国，但需大量进口铁矿石。巴西铁矿石资源丰富，是世界重要的铁矿石出口国。2010年4月13日，中国和巴西签订协议，共同出资在巴西里约热内卢附近建设一家年产500万吨钢材的大型钢铁厂，所产钢材主要用于巴西汽车制造、造船、石油开采等行业，部分输往中国。

说出与N河段相比较，M河段流量季节变化的差异，并分析原因。
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填空题

The central problem of economics is to satisfy the people’s and nation’s wants. The problem we are faced with is that our (1) , here identified as money, are (2) . The only way we can resolve our (3) is to make choices. After looking at our resources, we must examine our list of (4) and identify the things we need (5) , those we can postpone, and (6) we cannot afford. As individuals, we face the central problem involved in economics — deciding just how to allocate our limited resources to provide ourselves with the greatest (7) of our wants.
Nations face the same problem. As a country’s population (8) , the need for more goods and services grows (9) . Resources necessary to production may increase, but there are (10) enough resources to satisfy the total desires of a (11) . Whether the budget meeting is taking place in the family living-room, in the conference room of the corporation (12) of directors, or in the chamber of the House of Representatives in Washington, the basic problem still exists. We need to find (13) of allocating limited resources in order to satisfy unlimited wants.
A short time ago, economists divided goods into two categories, free and economic. The former, like air and water, were in (14) abundance that economists had no concern about (15) of scarcity and what to do about it. Today many of these "free goods" are in (16) very expensive to use. Pollution has made clean air and water expensive for producers who have to filter their waste products, for consumers who ultimately pay for the producers’ extra costs, and (17) tax-payers who pay for the government’s involvement in cleaning the environment.
In the 1990s, almost all goods are (18) . Only by effort and money can they be (19) in the form people wish.
Meeting the needs of people and the demands from resources available leads to the basic activity of production. In trying to (20) unlimited wants from limited economic goods, production leads to new problems in economics.
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