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
46
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.
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
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/aK9O777K
0
考博英语
相关试题推荐
I’venever______thetheorythatpeoplearemoreimportantthananimals.
Vitaminsareorganiccompoundsnecessaryinsmallamountsinthedietforthenormalgrowthandmaintenanceoflifeofanimals,
Vitaminsareorganiccompoundsnecessaryinsmallamountsinthedietforthenormalgrowthandmaintenanceoflifeofanimals,
Vitaminsareorganiccompoundsnecessaryinsmallamountsinthedietforthenormalgrowthandmaintenanceoflifeofanimals,
Asweareonthepointof______someimportantbusinesswiththem,weshouldliketoknowexactlyabouttheircreditstanding.
AmericanfootballandbaseballarebecomingknowntotheBritishpublicthroughtelevised______fromtheUnitedStates.
ThereislittlereasontobelievethattheUnitedStateswill______fromitsstatedgoalofregimechangeinIraq.
Colorisveryimportanttomostanimalsforithelpsthemtogetalongintheworld.Color【21】tomakeananimaldifficultforit
Colorisveryimportanttomostanimalsforithelpsthemtogetalongintheworld.Color【21】tomakeananimaldifficultforit
Thecommitteeistotallyopposed______anychangesbeingmadeintheplans.
随机试题
风湿热多见于哪一种致病微生物感染后发生的一种自身免疫性疾病
A、二尖瓣脱垂B、二尖瓣狭窄C、主动脉瓣狭窄D、感染性心内膜炎E、主动脉瓣关闭不全患者女性,20岁,胸骨左缘第4肋间可闻及喀喇音,心尖部可闻及收缩中晚期杂音
小儿腹泻发病率高的年龄组是
甲、乙、丙是挚友,三人合伙搞运输,后来生意越做越大,因为利润分配问题,三人逐渐有了隔阂。且三人对共有的样态没有约定,彼此间对当初的出资额也争执不下,三人的矛盾终于全面爆发。甲和乙协商将主厂房进行整体装修,丙表示不同意。因为一次好的商机,甲和丙决定将其全部财
根据代理委托方的不同,房地产经纪机构的代理可分为三种形式,其中不包括()。
下列选项中,不属于财产保护控制的是()。
方程y’sinx=ylny满足条件=e的特解是
项目经理花在沟通上的时间占()。
考生文件夹下有一个数据库文件“samp3.accdb”,其中存在已经设计好的窗体对象“fTest”及宏对象“ml”。请在此基础上按照以下要求补充窗体设计。设置命令按钮bTest的单击事件属性为给定的宏对象ml。
Idon’tremembersayinganythinglikethat.Youarepurposely______mywordstoproveyourpoint.
最新回复
(
0
)