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
40
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.
A rocket might miss its target,by a "wide margin". This means the rocket missed the target____.
选项
A、because of mechanical failure
B、by a great deal
C、by a small distance
D、because the target moved
答案
B
解析
题目问:火箭可能会错过一个“有广泛回旋余地“的目标,这句话意味着什么?本题可用排除法。A项“由于机械故障”,C项“距离短”,D项“因为目标移动”都不是文中所提原因。因此只有B项为正确答案。
转载请注明原文地址:https://kaotiyun.com/show/K1LO777K
0
考博英语
相关试题推荐
Shouldwecareifover150knownspeciesofanimalshave【1】fromtheearthinthelastfiftyyears?Shouldwebeconcernedthatt
Bigcitiestodayareconfrontedwithveryseriousproblems.Transportisa【1】difficulty:someplannersbelievein【2】transportsy
Sociologistsusethetermpowertorefertothecapacityofpeopleorgroupstocontrolorinfluencetheactionsofothers,whet
Ithinkyoucantakea(n)______languagecoursetoimproveyourEnglish.
Whenhefirststartedinuniversity,hereallyfeltat______withhismajor—economics.
Bankingandfinancialsystemsfilledwith______andcorruptionhindertheregion’ssuccess.
Thecompanywill______toitsagreement,nomatterhowcostlytheprocessmaybe.
Anewbiotechnologyprocedurethatcouldbecomecommerciallyavailableinaslittleastwotofouryearsis"transgenosis",whic
Investmentinthepublicsector,suchaselectricity,irrigation,quarrying,publicservicesandtransport(excludingvehicles,
Parentswhobelievethatplayingvideogamesislessharmfultotheirkids’attentionspansthanwatchingTVmaywanttoreconsi
随机试题
下列有关我国外国法查明问题说法不正确的是:
担保人必须是第三人的担保方式是( )。
关于企业成长期财务战略的描述中正确的是()。
我国古代律调中存在着两类调名体系分别是“为调”和()。
根据以下资料。回答问题。下面是对某市银行文明服务满意度的调查报告,问卷填写人对银行服务各项目的满意评价采用五级评分的方法进行,其中5分表示满意、4分表示较满意、3分表示一般、2分表示不太满意、1分表示不满意。满意率为“满意”和“较满意”的比率之和,满意度
婴儿期的记忆缺失现象,是指婴儿不能记住生命中最初的两年或三年里发生的事件。以往对这一现象的解释是:婴儿这一时期不能形成持久的关于自身经验的表征,即没有相关的记忆的存在,因此无法利用早期记忆。但近来的研究却发现事实并非如此,婴儿能够回忆较早的经验,并且在婴儿
为了提高公民的身体素质。本市设立了一条20公里的徒步路线,取得了很好的反响,领导决定再加开五条路线。让你负责路线的选取工作,你将如何开展?
在英国教育体系中增加职业技术教育一轨的文件是()
商店销售10台电冰箱中有3台次品,已售出1台,在余下的电冰箱中任取2台发现均为正品,则原先售出的1台为次品的概率为_________.
设f(x)=∫0x(ecist一e-cost)dt,则()
最新回复
(
0
)