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 Earth has a force that pulls things toward itself. We call this force gravity(地心引力). This is something we live with all the
The Earth has a force that pulls things toward itself. We call this force gravity(地心引力). This is something we live with all the
admin
2013-06-11
71
问题
The Earth has a force that pulls things toward itself. We call this force gravity(地心引力). This is something we live with all the time, and we take it for granted and hardly ever think about it. But it is a most important factor in rocket operation and must be overcome if we are to get anywhere in space, or off the ground at all.
Take the throwing of a ball as an example. The harder the ball is thrown, the faster and higher it will go. What is the secret? It’s speed. If we could throw the ball hard enough it would go up and up forever and never come down. The speed at which it would have to be thrown to do this is known as escape speed. Of course, we cannot throw a ball hard enough because the speed required to escape completely from’ the Earth’s gravity is seven miles per second, or over twenty-five thousand miles per hour.
Once escape speed has been reached by a spacecraft(宇宙飞船), no further power is needed. A rocket aimed at the Moon, for instance, will "coast"(滑行) the rest of the way because the Earth’s gravity cannot then pull it back, and there is no air resistance(阻力) in space to slow it down. This "coasting" is known as "free fall". That does not mean the rocket is falling down towards the Earth but that it is traveling freely in space without the aid of power, like a bicycle coasting downhill.
Free fall is an important feature of space travel: it would be impossible to carry enough fuel to provide powered flight all the time.
选项
A、To travel as fast as it can.
B、To overcome the Earth gravity.
C、To get away from the air resistance.
D、To have strong power in its operation.
答案
B
解析
从文章的第一段最后一句"地心引力是火箭飞行中的一个重要因素,如果我们想到达太空或者离开地球,我们就必须脱离地心引力",可以得出本题的答案应为B。
转载请注明原文地址:https://kaotiyun.com/show/E4rK777K
本试题收录于:
大学英语三级B级题库大学英语三级分类
0
大学英语三级B级
大学英语三级
相关试题推荐
Whendidthespeakerlearntosmoke?Thespeakerlearnstosmokeat______.Whyissmokingsoattractivetoyoungpeople?Bec
Forwhomisthepassageintendedto?Whatisthewritertryingtotellusthroughtheexampleinthelastparagraph?
Avisitortoourwebsite,www.riterate.ca,isnotrequiredtoexposeanypersonalinformation,suchasname,address,orteleph
Theystopped______(talk),becausetheteachercamein.
A—InternationalMarketPriceB—LandingChargesC—ApplicationNumberD—CurrentPriceE—FavorableBalanceofTradeF—CustomsDuty
NEWYORK—ThepeopleatUNICEF’s(联合国国际儿童教育基金会的)OperationCenterhavebeenworkingaroundtheclocktoarrangethereliefefforts
A--letterofintroductionB--masstourismC--ink-and-washpaintingD--travelagencyE--hospitalityindustryF--ma
ProverbsarequitecommoninspokenEnglish.Wedonotnormallyputtheminacompositionorletter.Sometimesitis(11)ify
A—UnitedNationsEnvironmentProgrammeB—WorldHealthOrganizationC—WorldMeteorologicalOrganizationD—World
A、Yourbikeisold.B、Intheshop.C、Atthestreetcomer.D、Motherboughtitforme.C
随机试题
在花盘的角铁上加工工件时,转速不宜太低。()
A.普鲁卡因B.利多卡因C.丁卡因D.布比卡因(2014年第145题)毒性反应最小的局麻药是
女孩,住在山区,平时多:病。检查,面颊部还有少量脂肪,心肺(一);腹壁皮下脂肪薄。山区无称重的磅秤。在谈条件下,评定营养不良只能依靠澜量臂围。该小儿以前按规定完成计划免疫。该年龄应复种以下哪一种疫苗
半夏泻心汤所治心下痞是由何因所致
妊娠慎用的中成药是()。
下列说法中,错误的有()。
风险衡量是在风险识别的基础上衡量潜在损失的规模和损失发生的可能性,主要采取( )来衡量。Ⅰ.损失概率Ⅱ.损失金额的数学期望Ⅲ.损失的数学期望Ⅳ.损失变量的方差Ⅴ.损失的变异性
在(x2+2)5的展开式中x4的系数是().
某地发生恐怖事件,在应对处置恐怖事件的过程中,下列做法错误的是()。
为客观反映我国电子商务发展状况,国家统计局服务业统计司利用企业“一套房”平台,通过联网直报的方式,对30.8万家企业的电子商务情况进行了调查。2012年,调查的30.8万家企业电子商务交易额为28825.2亿元,比上年增长17.6%(按可比口径,下同)。
最新回复
(
0
)