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
61
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.
This passage deals mainly with______.
选项
A、the gravitational pull of the Earth and the moon
B、the factors involved in firing a rocket into the outer-space
C、the gravitational fields of the Earth and the moon
D、the speed and direction of a rocket traveling in the outer-space
答案
A
解析
综观全文,本篇文章主要是关于地球和月球的地心引力问题,因此A项为正确答案。
转载请注明原文地址:https://kaotiyun.com/show/bGIO777K
0
考博英语
相关试题推荐
•ReadthetextbelowabouttheDisneycompany.•Inmostofthelines(34-45)thereisoneextraword.Itiseithergrammaticall
Readthearticlebelowaboutmanagingacrosscultures.ChoosethebestwordorphrasetofilleachgapfromA,B,CorDon
Lookatthestatementsbelowandthearticleaboutmeetingsontheoppositepage.Whichsection(A,B,CorD)doeseachstate
Howmanyaretherequalitycontrolinspectionpoints?Howtocheckthequalityduringproduction?
ThemanagingDirectorfeelstheymust______.ThemanagingDirectorgotanothermeetingat
WhatproblemdidBrianhavewithhissandwichbusiness?Geraldinestartedhersandwichbusinessbecauseshe
Whatisthemostimportantaspectofamanager’sjob?WhatdidthemanagersinWesternElectricdotoimprovethecompany’sper
Lookatthenotesbelow.Someinformationismissing.Youwillhearawomanorderingsomeelectricalequipment.Foreachquestio
FeaturesofWarehouseManagementSystemWarehouseManagementSystemsaregainingimportancesimilartothatofothersoftwar
Olgahadalwaysenjoyedthecharacter-centeredbookswrittenbyAdeleKwanandwantedtoreadanotheroneifitseemedinteresti
随机试题
基本生产过程
牙震荡的处理方法首选
医院药事管理委员会是
关于肾功能检查,下列哪些描述正确()。
除圆管涵和箱涵外,单孔跨径小于()m的泄水或通行的小型构造物是涵洞。[2010年真题]
注册会计师在期中实施进一步审计程序也存在很大的局限性,下列有关局限性的说法不恰当的是()。
有些课题主要包含高度有结构的知识和技能,如果教学目标是要求学生尽快地掌握这种知识和技能,则宜于采用()。
幂级数的和函数及定义域是______·
MostpeoplewhodevelopLymedisease,atick-borneinfectionthat’sendemicinpartsoftheNortheastandMidwest,areeasilycu
TheMillenniumSeedBankProjectOneofthelargestconservationprojectseverundertaken;thisinternationalcollaboration
最新回复
(
0
)