首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
The gravitational pull of the Earth and moon is important to us as we attempt to conquer more and more of outer-space. Here’s wh
The gravitational pull of the Earth and moon is important to us as we attempt to conquer more and more of outer-space. Here’s wh
admin
2005-11-28
74
问题
The gravitational pull of the Earth and moon is important to us as we attempt to conquer more and more of outer-space. Here’s why.
As a rocket leaves the Earth, the pull of the Earth on it becomes less and less as the rocket roars out into space. If you imagine a line between the pull of the Earth and the moon, there is a point somewhere along that line, nearer to the moon than to the Earth, at which the gravitation pull of both the Earth and the moon on an object is just about equal. An object placed on the moon side of that point would be drawn to the moon. An object placed on the Earth side of that point would be drawn to the Earth. Therefore, a rocket need to be sent only to this "point of no return" in order to get it to the moon. The moon’s gravity will pull it to the rest of the way.
The return trip of the rocket to the Earth is, in some ways, less of a problem. The Earth’s gravitational field reaches far closer to the moon than does the moon’s to the Earth. Thus it will be necessary to fire an Earthbound rocket only a few thousand miles away from the moon to reach a point where the rocket will drift to earth under the Earth’s gravitational pull.
The problem of rocket travel is not so much concerned with getting the rocket into space as it is with guiding the rocket after it leaves the Earth’s surface. Remember that the moon is constantly circling the Earth. A rocket fired at the moon and continuing in the direction in which it was fired would miss the moon by a wide margin and perhaps continue to drift out into space until "captured" in another planet’s gravitational field. To reach the moon, a rocket must be fired toward the point where the moon will be when the rocket has traveled the required distance. This requires
precise
calculations of the speed and direction of the rocket and of the speed and direction of the moon.
For a rocket to arrive at a point where the moon’s gravity will pull it the rest of the way, it must reach a speed called velocity of escape. This speed is about 25,000 miles per hour. At a speed less than this, a rocket will merely circle the Earth in an orbit and eventually fall back to the Earth.
Precise
calculations are______.
选项
A、good guesses
B、simple problems
C、big errors
D、exact
答案
D
解析
文中precise的意思是“精确的,准确的”,D项exact“精确的,准确的”与之相符。
转载请注明原文地址:https://kaotiyun.com/show/zGIO777K
0
考博英语
相关试题推荐
BuildaTeamCreatingtherightteamisimperativetoyoursuccess.Ateamiscomprisedofpeoplewhocanbringnecessarysk
•Readthearticlebelowaboutsuggestionsforeffectivemeetingsandthefollowingquestions.•Foreachquestion(13-18),marko
•ReadthearticlebelowaboutAmericanconsumers’borrowingstyles,andthequestionsontheoppositepage.•Foreachquestion
Readthetextbelowaboutacompany’sapproachtosocialresponsibility.Inmostofthelines(34-45),thereisoneextrawor
Readthearticlebelowaboutdevelopmentsatabank.Choosethebestsentencefromtheoppositepagetofilleachofthegap
ThemanagingDirectorfeelstheymust______.ThemanagingDirectorgotanothermeetingat
JameLewis,yourboss,hascalledameetingonThursday,butyoucannotattendbecauseyouwillbeawayataconference.Write
Youareunabletoattendanimportantmeetinginyourcompanyasyouwillvisitaninternationaltradefair.Writeamemotothe
Satellitetechnology(means)(thatpeople)canwatchthesameTVprogramsin(other)partsoftheworld(like)inAmerica.
Heobviouslydisplayedagreat______forsomeofyourpoems.
随机试题
神经纤维中相邻两个锋电位的时间间隔至少应大于其
捻转泻法为指
正常胃液为
吸宫术后注意事项,不正确的是
下图为某沿城市道路建设的小商品市场总平面简图,导入顾客人流最差的方案是()。
对于刚开始进行组合管理的商业银行,可主要设定()的集中度限额。
在C国,卫浴产品属于兼具功能性和时尚性的产品。其功能性和外观时尚性的不同导致了不同企业之间的差异。T公司、K公司都为知名的国际品牌企业。设计研发水平高,在品牌塑造上投入较大,具有很强的品牌影响力,其提供的产品和服务的特征是追求顾客的高端体验,满足了顾客对
小明骑自行车到朋友家聚会,一路上他注意到每隔12分钟就有一辆公交车从后边追上。小明骑着骑着突然车胎爆了,他只好以原来骑车三分之一的速度推着车往回走,这时他发现公交车以每隔4分钟一辆的频率迎面开过来,公交车站发车的间隔时间到底为多少?
(上海财大2012)在下列指标中反映企业营运能力的是()。
在软件工程中,白箱测试法可用于测试程序的内部结构。此方法将程序看做是()。
最新回复
(
0
)