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
2013-01-15
19
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 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.
According to the passage, the most difficult task of firing a rocket is ______ .
选项
A、to get the rocket into the space
B、to calculate the rocket’s velocity of escape
C、to guide the rocket after it leaves the Earth’s surface
D、to identify the gravitational fields of the Earth and the moon
答案
C
解析
本题的依据句是“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.”从中可知C项为正确答案。
转载请注明原文地址:https://kaotiyun.com/show/iK9O777K
0
考博英语
相关试题推荐
AlthoughmostuniversitiesintheUnitedStatesareonasemestersystemwhichoffersclassesinthefallandspring,someschoo
Oneofthemanytheoriesaboutalcoholismisthelearningandreinforcementtheory,whichexplainsalcoholismbyconsideringalc
Vitaminsareorganiccompoundsnecessaryinsmallamountsinthedietforthenormalgrowthandmaintenanceoflifeofanimals,
Vitaminsareorganiccompoundsnecessaryinsmallamountsinthedietforthenormalgrowthandmaintenanceoflifeofanimals,
Vitaminsareorganiccompoundsnecessaryinsmallamountsinthedietforthenormalgrowthandmaintenanceoflifeofanimals,
Mybosshasalwaysattendedtothe______ofimportantbusinesshimself.
Anxietyisbelievedto______diabetesbyraisinglevelsofthestresshormonecortisolwhichregulatesinsulinandblood-sugar
Colorisveryimportanttomostanimalsforithelpsthemtogetalongintheworld.Color【21】tomakeananimaldifficultforit
Thecommitteeistotallyopposed______anychangesbeingmadeintheplans.
随机试题
根据我国公务员法,下列属于参照公务员制度进行管理的机关是
风水初期的主证是
在十二经脉走向中,足之三阴是
承包人报送的竣工结算报表由( )审核。
职工出差回来报销差旅费800元,出差前已预借1000元,剩余款项交回现金。企业采用专用记账凭证方式,对于报销这项经济业务应直投的记账凭证是()
许多场外交易发生在投资者和()之间。
E公司为一家上市公司,为了适应外部环境变化,拟对当前的财务政策进行评估和调整,董事会召开了专门会议,要求财务部对财务状况和经营成果进行分析。相关资料如下:资料一:公司有关的财务资料如下表所示:说明:“*”表不省略的数据。资料
以下各项中()是政府非常设机构。
曾就读于科技大学少年班,被人们称为“神童”“未来的诺贝尔奖获得者”的谢彦波,因不能处理好与导师的关系,被迫中途结束了在美国的留学生涯。从这段文字中可以推出:
美国前总统胡佛对其继承者实行《工业复兴法》极为不满,称之为法西斯行径。这番话主要是针对这一法令()。
最新回复
(
0
)