问题 选择题

下列说法正确的是(  )

A.第一宇宙速度是所有人造卫星运行的最大速度

B.卫星的发射速度与运行速度大小相等

C.卫星离地面越低,发射速度越大,而运行速度越小

D.绕地球飞行的航天飞机中,用弹簧秤挂一物体,其示数为零

答案

A、第一宇宙速度是绕地球做匀速圆周运动的最大速度,当卫星绕地球沿椭圆轨道运动时,其发射速度大于第一宇宙速度,即卫星在近点运动的速度大于第一宇宙速度,故A错误;

B、卫星的发射速度是卫星进入近地轨道时的速度,卫星的运行速度是卫星在其轨道运行时的速度,向高轨道上发射卫星时其发射速度大于其运行速度,故B错误;

C、发射卫星的最小发射速度为第一宇宙速度,也是卫星到达近地轨道时的速度,根据能量关系可知,卫星轨道高度越大所需能量越多,则其发射速度越大,卫星轨道高度越低发射速度越小,故C错误;

D、绕地球飞行的航天飞机万有引力提供圆周运动向心力,飞机中的物体处于完全失重状态,故物体对弹簧秤的拉力为0,所以D正确.

故选:D.

阅读理解

阅读理解。

                                                               To face the music

     Like every language, American English is full of special expressions, phrases that come from the

day-to-day life of the people and develop in their own way. Our expression today is "to face the music".

     When someone says,"well, I guess I'll have to face the music," it does not mean he's planning to go

to the concert. It is something far less pleasant, like being called in by your boss to explain why you did

this and did that, and why you didn't do this or that. Sour music indeed, but it has to be faced. At

sometime or another, every one of us has had to face the music, especially as children. We can all

remember father's angry voice,"I want to talk to you." and only because we did not obey him. What an

unpleasant business it was!

     The phrase "to face the music" is familiar to every American, young and old. It is at least 00 years old.

And where did this expression come from? The first explanation comes from the American novelist,

James Fenimore Looper. He said, in 85, that the expression was first used by actors while waiting in the

wings to go on the stage. When they got their cue to go on, they often said, "Well, it's time to face the

music." And that was exactly what they did - facing the orchestra which was just below them. And an

actor might be frightened or nervous as he moved on to the stage in front of an audience that might be

friendly or perhaps hostile, especially if he forgot his lines. But he had to go out. If he did not, there would

be no play. So the expression "to face the music" come to mean "having to go through something, no matter

how unpleasant the experience might be, because you knew you had no choice."

     Other explanations about the expression go back to the army. When the men faced an inspection by

their leader, the soldiers would be worried about how well they looked. Was their equipment clean, shinny

enough to pass the inspection? Still the men had to go out and face the music of the band as well as the

inspection. What else could they do?

     Another army explanation is more closely related to the idea of facing the results and accepting the

responsibility for something that should not have been done. As, for example, when a man is forced out

of the army because he did something terrible, he is dishonored. The band does not play. Only the drums

tap a sad, slow beat. The soldier is forced to leave, facing such music as it is and facing the back of his

horse.

1. How many ways does the phrase"to face the music" comes from?

A.1

B. 2

C. 3

D. 4

2. What's the meaning of "to face the music?"

A. To face something far less pleasant.

B. To face the stage.

C. To face the back of one's horse.

D. To face one's leader.

3. Which of the following is a situation of facing the music?

A. When we are playing basketball.

B. When we are making a speech.

C. When we are having a party.

D. When we are talking with somebody.

4.  The underlined word "hostile" means _______.

A. unfriendly

B. useless

C. unkind

D. unnecessary

问答题 简答题