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
39
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
After______seemedanendlesswait,itwasherturntoenterthepersonnelmanager’soffice.
Shouldwecareifover150knownspeciesofanimalshave【1】fromtheearthinthelastfiftyyears?Shouldwebeconcernedthatt
Shouldwecareifover150knownspeciesofanimalshave【1】fromtheearthinthelastfiftyyears?Shouldwebeconcernedthatt
Ifitwereonlynecessarytodecidewhethertoteachelementarysciencetoeveryoneonamassbasisortofindthegiftedfewan
Therearethreeseparatesourcesofhazard【1】totheuseofnuclearreactiontosupplyuswithenergy.Firstly,theradioactivem
AlltherecentnewsonAIDSisbad.ThedeathofRockHudson【1】publicconcernaboutthe【2】almosttothepointofpanic.Nowgene
Themostexcitingkindofeducationisalsothemostpersonal.Nothingcan【1】thejoyofdiscoveringforyourselfsomethingthat
Mostofthepeoplewhoappearmostoftenandmostgloriouslyinthehistorybooksaregreatconquerorsandgeneralsandsoldiers
Oneofthebasiccharacteristicsofcapitalismistheprivateownershipofthemajormeansofproduction—capital.Theownership
Ofthegreatvarietyofopinionsconcerning"marriageformoney",thefollowingthreeareimportantwithreferencetothedevelopm
随机试题
怎样理解素质教育的内涵?
A.俯卧位B.仰卧位C.右侧卧位D.左侧卧位E.膝胸卧位慢性细菌性痢疾行保留灌肠时采取
胃癌在下列哪种情况下不能行根治性手术
依据《建设项目竣工环境保护验收管理办法》,建设单位申请建设项目竣工环境保 护验收应当提交的验收材料有()。
钢筋的混凝土保护层厚度所起的主要作用有()。
下列各项属于工业企业主营业务收入的是( )。
某企业2010年10月发生如下经济业务,根据所给的经济业务编制会计分录。10月6日,上述材料到达,并验收入库。
在一定时期和一定业务量范围内,关于固定成本与变动成本下列说法正确的有()。
有研究表明,同卵双生子即使生长在不同的家庭环境中,他们的智商也有很高的相关。这说明了()。
Theinformationwaslateradmitted______obtainedfromunreliablesources.
最新回复
(
0
)