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
2012-06-18
75
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 man 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.
It can be seen that if a rocket misses its target, it keeps on traveling through space until_______.
选项
A、it burns up
B、it is caught in the gravitational field of another planet
C、it is brought back to the Earth by scientists
D、it runs out of fuel
答案
B
解析
本题的依据句是“A rocket fired at the moon and continuing in the direction in which it was firedwould miss the moon by a wide margin and perhaps continue to drift out into space until‘captured’in another planet’s gravitational field.”从中可知B项为正确答案。
转载请注明原文地址:https://kaotiyun.com/show/28nO777K
0
考博英语
相关试题推荐
Title:TheEffortsofMarketsonEnvironmentTimelimit:40minutesWordlimit:nolessthan150words(notincludingth
ThegravitationalpulloftheEarthandmoonisimportanttousasweattempttoconquermoreandmoreofouter-space.Here’swh
Alternatively,researchersseekingaccesstoidentifiable,recordsorspecimenscanuse"expedited"IRBreview,inwhichoneboa
Schoolintegrationplansthatinvolvebusingbetweensuburbanandcentralcityareashavecontributed,accordingtoarecentstu
Theballadandthefolksonghavelongbeenrecognizedasimportantkeystothethoughtsandfeelingsofapeople,butthedime
IntheUnitedStatesandinmany【51】countriesaroundtheworld,therearefourmainwaysforpeopletobeinformed【52】develo
Hisparentsgavemanyexpensivetoysasakindof______forhislamenessandinabilitytoplayactivegames.
OverandoverinWaroftheWorlds,heevokesthesensation,morefamiliarfromdreamsthanmovies,______anotherworldlyentity
Therecanbenoquestionaboutthedangersofheroinuse.Whatmaystartoutinnocentlyenoughasadesiretoexperienceanewk
PitythosewhoaspiretoputtheinitialsPhDaftertheirnames.After16yearsofcloselysupervisededucation,prospectivedoc
随机试题
OurdaughterBrennawasbornin2011withaverysevere,raregeneticskinillness【C1】______HarlequinIchthyosis(丑角样鱼鳞病).Itme
患儿男,3岁。因肺炎住院治疗,出现焦虑表现。此期患儿对疾病的认识描述正确的是
患者,女性,48岁,理发员。下肢酸胀、沉重5年,活动或休息后减轻。体检见小腿内侧有蚓状团块,足靴区有色素沉着。若对该患者行手术治疗,术后的主要护理措施有
高于原地面的填方路基称为()。
园林绿化工程不包括()工程。
根据企业所得税的规定,以下适用25%税率的是()。
“草原天路”是一条建于2012年9月的县级公路,全长132.7千米。这条公路因沿途风景壮丽,被自驾游游客发现。游客通过微信和微博不断转发相关信息,使得“草原天路”的旅游价值凸显,声名远播。2013年年底,该条公路所属A县政府发文,称2014年将倾全县之力打
2014年1月20日,A公司与B公司签订购买B公司持有的C公司(非上市公司)80%股权的合同。合同约定:以C公司2014年5月30日评估的可辨认净资产公允价值为基础,协商确定对C公司80%股权的购买价格;合同经双方股东大会批准后生效。发生此业务前,A公司与
选择性执法就是只将法律适用于某一时期或者某一些人,也就是选择特定时段,选择特定对象,选择特定法律法规,期望达到特定目的。例如:忽然要整治道路交通,于是对某些依惯性横穿马路的行人每人罚款50元,弄得“路上行人欲断魂”。交通整治期一过,行人再横穿马路就无人过问
Idoubt______.
最新回复
(
0
)