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
2015-01-09
86
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 Earth-bound 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.
Precise calculations are_____.
选项
A、good guesses
B、simple problems
C、big errors
D、exact
答案
D
解析
题目问:精确计算是什么意思?在这里,precise的意思是“精确的,准确的”。根据各项的意思,只有exact符合题意,exact的意思是“精确的,准确的”。所以,答案是D。
转载请注明原文地址:https://kaotiyun.com/show/d1LO777K
0
考博英语
相关试题推荐
Ifitwereonlynecessarytodecidewhethertoteachelementarysciencetoeveryoneonamassbasisortofindthegiftedfewan
Predictionsoflargepopulationsofrobotsinindustryhaveyettocometrue.Foradecadeormore,manufacturersofbigrobots
Predictionsoflargepopulationsofrobotsinindustryhaveyettocometrue.Foradecadeormore,manufacturersofbigrobots
BytheendoftheMiddleAgesthetechnologicalsystemscalledcitieshadlongsincebecomeacentralfeatureofWesternlife.I
Mostofthepeoplewhoappearmostoftenandmostgloriouslyinthehistorybooksaregreatconquerorsandgeneralsandsoldiers
Heaskedmetolendhimsomemoney,whichIagreedtodo,______thathepaidmebackthefollowingweek.
TogetfromKathmandutothetinyvillageinNepal,DaveIrvine-Hallidayspentmorethantwodays.Whenhearrived,hefoundvil
Lifeinsuranceisfinancialprotectionfordependentsagainstloss______thebread-winner’sdeath.
Imaginemyvexationwhentheysaidtheywouldcometodinnerandthendidn’tshow.
随机试题
下列检查不能反映心功能状态的是
下列不是四肢CT扫描适应证的是
A.丙硫氧嘧啶B.甲状腺素片C.利血平D.复方碘溶液E.131碘治疗常用的抗甲状腺药物是
男,65岁,患胆囊结石25年,3天前突然再次发作。45岁曾因胃溃疡做胃大部分切除术。
心肾不交而致不寐者,应选用的方法是
在统计中,()用于说明总体单位的数量特征。
经相关部门批准,甲公司于2018年1月1日按面值发行分期付息、到期一次还本的可转换公司债券1000万份,每份面值为100元。可转换公司债券发行价格总额为100000万元,发行费用为1600万元,实际募集资金已存入银行专户。发行时二级市场上与之类似的没有附带
注册会计师通过实施“检查外来账单与本单位有关账目的记录是否相符”这一审计程序,可能证实被审计单位管理层对财务报表的()认定。
下列关于WindowsXP文件名的说法,不正确的是()。
AdamSmith,writinginthe1770s,wasthefirstpersontoseetheimportanceofthedivisionoflaborandtoexplainpartofits
最新回复
(
0
)