已知月球质量与地球质量之比约为1 : 80，月球半径与地球半径之比约为1 : 4，则月球上的第一宇宙速度与地球上的第一宇宙速度之比最接近( )
A．9 : 2
B．2 : 9
C．18 : 1
D．1 : 18
答案：B
题目分析：第一宇宙速度是近地卫星的环绕速度，由
得
，
因此月球上的第一宇宙速度与地球上的第一宇宙速度之比：
。
故选B
点评：第一宇宙速度为贴近星球表面飞行的卫星的环绕速度，不但地球有第一宇宙速度，任何星球都有第一宇宙速度，计算思路都是相同的。
In the United States, engineering is a profession(职业) that has been historically under the control of men. Even today, it’s still true that few women become civil or chemical or mechanical engineers, but that’s something on www.EngineerGirl.org encouraging girls to change the present situation. Young women who visit the web site can find out about a great job choice they might not have considered. "Women are not well represented in engineering and in engineering education programs and then of course, down the road, in the engineering workforce. So only about 20 percent of engineering undergraduate degrees(本科文凭) go to women, and then only about nine percent of working engineers are women." Mary Mattis, the National Academy of Engineering, says "we know from the research that middle-school girls are at a critical point in their lives, and that it’s a time when we need to reach them, so this website aims to increase their awareness of interesting fields in engineering. On the other hand, it wants to make them understand what a wonderful productive and exciting job you can have as an engineer.” Engineering is a demanding course of study—there is a lot of science and math, for many girls and even boys that can be challenging. But Ms. Mattis says that the EngineerGirl website stresses that engineering can also be fun and exciting. "It’s about designing things. It’s about changing the world for people. It’s about making a difference. And, in addition, you can make a good living; you can be independent economically by becoming an engineer. All of those things are messages that girls need to get." While most engineers go into traditional fields such as mechanical and electrical engineering, the EngineerGirl site also emphasizes engineering jobs which are related to other fields such as bio-engineering, sports engineering and --- believe it or not—chocolate engineering. Even if you are not a girl in the target(目标) age group, there’s a lot of interesting information on the site, including biographies(自传)of some well-known women engineers.
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