首页
登录
职称英语
The Earth has a force that pulls things toward itself. We call this force gr
The Earth has a force that pulls things toward itself. We call this force gr
游客
2023-10-06
75
管理
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://tihaiku.com/zcyy/3075561.html
相关试题推荐
Thingsgotsobad(recent)______thathedecidednottogotohisoffice.recent
Harrycamein______.[br]Theauthordidn’tlooktowardthestairsagainuntil
[originaltext]Man:Areyougettingouttoseethings?Woman:Well,I’mverybus
Whenpeoplebecomegoodatdoingthethingstheyliketheyfindthemselves.
Ihavea(plenty)______supplyofthingstokeepthechildrenhappywhenwego
Tonyisverydisappointed______theresultsoftheexam.A、towardB、withC、onD、
Therehavebeenmanygreatinventions,thingsthatchangedthewaywelive.A、有许多
Top4ThingstoDoBeforeYouGoTr
Top4ThingstoDoBeforeYouGoTr
Heinsistedon(do)______thingsinhisownway.doingon为介词,其后接动名词作其宾语。
随机试题
TheAsian(1)hastakenitstollonHongKong’stouristindustry,(2)offor
DreamFunctionsDreamingisacommonphenomenon.
When,accordingtoMrs.Hammer,isthephoneinterviewlikelytotakeplace?[br
Itiscommonknowledgethatmusiccanhaveapowerfuleffectonour【B1】_____
下列可以作为接地装置的是A.暖气管道 B.避雷针的接地线 C.煤气管道 D
女性30岁,间断皮疹、关节痛2年,化验尿:尿蛋白(++),红细胞5~10个/HP
A基金拟进行医疗器械制造行业的投资,正在对业务及产品类似的Y、Z两个公司尽调。其
在变量Y表示对X进行回归分析时,根据10对观测值(xi,yi),i=1,2
政府委托推销机构利用金融市场直接售出国债,这种发行国债的方法是()。A:承受法
生态等级评价将生态风险评价分为( )三部分。A.初级评价 B.高级评价 C
最新回复
(
0
)