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
2013-01-15
12
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 Earth 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 be sent only to this "point of no return" in order to get it to the moon. The moon’s gravity will pull it the rest of the way.
The return trip of the rocket to 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 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 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。因此A项为正确答案。
转载请注明原文地址:https://kaotiyun.com/show/ZK9O777K
0
考博英语
相关试题推荐
Vitaminsareorganiccompoundsnecessaryinsmallamountsinthedietforthenormalgrowthandmaintenanceoflifeofanimals,
Vitaminsareorganiccompoundsnecessaryinsmallamountsinthedietforthenormalgrowthandmaintenanceoflifeofanimals,
Vitaminsareorganiccompoundsnecessaryinsmallamountsinthedietforthenormalgrowthandmaintenanceoflifeofanimals,
Vitaminsareorganiccompoundsnecessaryinsmallamountsinthedietforthenormalgrowthandmaintenanceoflifeofanimals,
Vitaminsareorganiccompoundsnecessaryinsmallamountsinthedietforthenormalgrowthandmaintenanceoflifeofanimals,
Vitaminsareorganiccompoundsnecessaryinsmallamountsinthedietforthenormalgrowthandmaintenanceoflifeofanimals,
AmericanfootballandbaseballarebecomingknowntotheBritishpublicthroughtelevised______fromtheUnitedStates.
IntheUnitedStatesatthetimeofWorldWarⅡ,(When)soldierswerescreened(formilitaryservice)thearmydefined(aminima
Colorisveryimportanttomostanimalsforithelpsthemtogetalongintheworld.Color【21】tomakeananimaldifficultforit
随机试题
刮削完毕后的井下套管内径必须畅通无阻。()
测量结果有效是指()
A.快速耐受性B.成瘾性C.耐药性D.反跳现象E.高敏性长期应用氢化可的松突然停药可发生
我国《公路隧道施工技术规范》规定,甲烷(CH4)按体积计不得大于()。
根据形态理论,股价移动的规律是完全按照( )决定的。
甲公司系商贸企业(增值税一般纳税人),适用的增值税税率为17%,题目中收入均为不含税收入。存货发出计价采用先进先出法核算。2017年4月发生的经济业务如下:(1)1日,结存A商品500件,单位成本为350元,已计提存货跌价准备10000元。(2)5日,
在谈判过程中,常用的限制性因素主要有()。
根据岗位数量、岗位工作量和劳动者工作效率来核算定员人数的方法属于()。
模块是以函数过程或______为单元的集合方式存储。
StudentsarecalledinAmericanclasses______。
最新回复
(
0
)