题干

发射地球同步卫星时,先将卫星发射至近地圆轨道1,然后经点火,使其沿椭圆轨道2运行,最后再次点火,将卫星送入同步圆轨道3. (如图所示)。则卫星分别在1、2、3轨道上运行时,以下说法正确的是 (     )

A:卫星在轨道3上的速率大于在轨道1上的速率

B:卫星在轨道1上的角速度大小等于在轨道2上经过Q点时的角速度

C:卫星在轨道3上具有的机械能大于它在轨道1上具有的机械能

D:卫星在轨道3上的向心加速度大于它在轨道2上经过P点时的加速度

上一题 下一题 0.0难度 选择题 更新时间:2018-11-04 01:23:31

答案(点此获取答案解析)

C

同类题4

      London has a new magazine. But it is not printed(印刷) on paper. Everyone who has a television can receive it because it is on TV.
In order to read this magazine you have to have a decoder (解码器). Each page of it is numbered, so you only have to dial the number to choose which subject you want to read about. There are all kinds of information ---everything is included from cooking to the latest sports news.
       If you want to read the news, the first thing you have to do is to turn to the back page, which has an easy-to-remember page number, 100 for example. Then you start choosing what you want to read. The news is on page 101 to 109, so you put in the numbers and the news appears written across your screen. Perhaps you want to go out in the afternoon, so you press 181, and a brightly colored weather map appears on the screen. But the weather is terrible, so you decide to go shopping and dial 162 for a list of the week’s best bargains. But should you drive or take the train? To answer that question you only have to press 189 for the traffic report. It is very simple to use. But probably the best thing about the service is that it is being updated all the time. Journalists type new material directly onto the screen and the whole pages of the magazine can be replaced in minutes.
         London already has three services. One, sent out by TV, is called ORACLE while the other two, on BBC, are called CEEFAX because they let you see facts. Although CEEFAX and ORACLE have been operating for some time, they have not been well publicized(宣传). BBC engineers do not think that their idea will ever replace books and newspapers because they can be taken with you everywhere. But many people would agree that is a breakthrough(突破) as great as the invention of printing, which could not just change our reading habits but our whole way of life.