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
2011-01-26
29
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 fining 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://www.kaotiyun.com/show/TnBO777K
0
考博英语
相关试题推荐
YouaregoingtospendholidaysinHawaiiinJune.Suddenlyyoureceivedaletterfromanimportantcustomer,Mr.EltonDeland,
Youareunabletoattendanimportantmeetinginyourcompanyasyouwillvisitaninternationaltradefair.Writeamemotothe
CommercialBanksCommercialbanksplayanimportantrole(29)national(30)。(31)theendofMay1995,Chinahas1
CommercialBanksCommercialbanksplayanimportantrole(29)national(30)。(31)theendofMay1995,Chinahas1
PleasenoteStaffshouldcontactthesupplier’stechniciansifthereisafaultandnotattempttorepairtheprinterthemselves
AllthemanagersarerequestedtoattendanimportantmeetingattheBoardMeetingRoomat08:00nextMonday.
FiveInterviewingFundamentalsThemostimportantthingtofindoutwhenyouinterviewsomeoneisifyouliketheperson.Yo
随机试题
人们跟随潮流,顺应风俗习惯的现象,称为()
A.胡萝卜苷B.水杨苷C.芦荟苷D.苦杏仁苷E.红景天苷能被碱水解的化合物是
我国的《银行卡管理办法》规定储值卡的面值不得超过人民币()
睾丸支持细胞的生理功能不包括
A.荆芥B.橘红C.甘草D.桔梗、白前E.紫菀、百部
[2008年第47题]建筑物需满足以下哪个条件时才能形成热压通风?
唐《户令》:“诸应分田宅者,及财物,兄弟均分。妻家所得之财,不在分限。兄弟亡者,子承父分。兄弟俱亡,则诸子均分。其未娶妻者,别与聘财。姑姊妹在室者,减聘财之半。寡妻妾无男者,承夫分。”唐《丧葬令》:“诸身丧户绝者,所有部曲、客女、奴婢、店宅、资财,并令近亲
Americaisoneofmanycountrieswherethestategivesaleg-uptomembersofcertainracial,ethnic,orothergroups【C1】______h
在下列关于VisualFoxPro常量的数据类型的描述中,正确的一条是______。
Today’scollegestudentsaremorenarcissisticandself-centeredthantheirpredecessors,accordingtoacomprehensivenewstud
最新回复
(
0
)