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
2013-01-12
25
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.
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
题目问:如果火箭不能进入目标会怎样?文章提到“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 driftout into space until“captured”in another planet’s gravitational field.”通过这句话可知,答案是B。
转载请注明原文地址:https://kaotiyun.com/show/qv9O777K
0
考博英语
相关试题推荐
Youareaskedtowriteacompositioninnolessthan150wordsaccordingtothechartgivenbelow.Remembertowriteclearlyon
Currentdatasuggestthatalthough______statesbetweenfearandaggressionexist,fearandaggressionareasdistinctphysiolo
Noonecouldcomeupwithaneasysolutiontothegovernment’spredicament—labor______whichiscausedbythewars.
71.ThemainimpressiongrowingoutoftwelveyearsonthefacultyofamedicalschoolisthattheNo.1healthproblemintheU
Wehaveatpresentnotany______ofthefurnitureasyourequired.
InthispartyouarerequiredtowriteacompositionentitledHowtoSolvetheEnergyProbleminnolessthan200words.Yourco
InthefirstyearorsoofWebbusiness,mostoftheactionhasrevolvedaroundeffortstotaptheconsumermarket.Morerecentl
The______ofthewordisunknown,butitiscertainlynotfromGreek.
Ipersonallyamoffendedbywhattheyhavetriedtodoinaverymisleadingwaywith,whatI’vesaidabouttwoofmypersonal___
Peoplewhoquestionorevenlookdownonthestudyofthepastanditsworksusuallyassumethatthepastisentirelydifferent
随机试题
凝固性坏死(coagulativenecrosis)
依法治国的主体是党。()
关于抗毒素的使用,错误的是
诊断癔症最重要的是
A.寒战、高热、出血并迅速衰竭B.头痛、呕吐,脑脊液可检出白血病细胞C.低热、乏力、颈部淋巴结肿大,切口不愈合D.低热、贫血、巨脾E.贫血、发热、无痛性淋巴结进行性肿大
患者,男性,68岁。2周来反复胸痛,发作与劳累及情绪有关,休息可以缓解。3小时前出现持续性疼痛,进行性加剧,伴气促,不能平卧。查体:血压110/70mmHg,心率120次/分,律齐,心尖部可闻及3级收缩期杂音,双肺散在哮鸣音及湿啰音。为确诊,该患者应首
一男性农民,4天前突然发热,头痛,面颈部潮红,全身酸痛,伴恶心、呕吐及腹泻,每日2~3次,按“感冒”治疗未见好转来诊。体温39.5℃,血压80/60mmHg,脉搏94次/次。最有助于诊断的化验检查是
当前各类安全生产问题错综复杂,但其中影响最大、危害最严重的主要有()。
固定资产的盘盈、盘亏均属于前期差错。()
案例:学习目标:(1)增强奔跑能力,发展心肺功能。(2)提高自主学练能力。(3)培养探究精神,提高合作学习的能力。学习内容:跑动性游戏。学习步骤:(1)教师给学生们三个排球,让学生自主创
最新回复
(
0
)