问题 选择题

某同学通过Internet查询“神舟”九号飞船绕地球运行的相关科技数据,从而将其与地球同步卫星进行比较,他了解到“神舟”九号飞船在圆周轨道上运转一圈大约需要90min,则“神舟”九号飞船在圆周轨道运行的过程中(   )

A.速率比地球同步卫星的小

B.角速度比地球同步卫星的小

C.离地面高度比地球同步卫星的低

D.向心加速度比地球同步卫星的小

答案

答案:C

题目分析:“神舟”九号飞船在圆周轨道上运转一圈大约需要90min,地球同步卫星的周期为24h,卫星做匀速圆周运动,万有引力充当向心力,则由所以“神舟”九号飞船离地面的高度比同步卫星离地面的高度低,C选项正确;由,“神舟”九号飞船在圆周轨道运行速率比地球同步卫星的大,所以A选项错误;由,“神舟”九号飞船在圆周轨道运行的角速度比地球同步卫星的大,所以B选项错误;由,“神舟”九号飞船在圆周轨道运行的加速度比地球同步卫星的大,D选项错误。

选择题
单项选择题

Oxford and Cambridge University Boat Clubs have both taken the opportunity to travel to Spain this month to train in less testing weather conditions than those which have, quite literally, already blown around the UK in January of 2007.

Each group of athletes has been focused on training to the maximum, working on technique and molding themselves into two potential fighting units per Club for the 2007 Boat Race, sponsored by Xchanging. One set will be in the Blue Boat for each club and one set will race as reserves in Isis, for Oxford, and Goldie, for Cambridge.

In these modern times, the Head Coach for each club has a huge input on selection even though the crew is still named by the President. Just twenty years ago the balance was not quite the same.

The year 1987 will always be remembered in the history of this great Race as the year of the "mutiny" at Oxford. It is a tale which has since been retold and reworked in both a book and a movie.

This was the season for which mature Scottish student, Donald Macdonald, was elected President, having all ready won a Blue in 1986. Macdonald re-appointed Daniel Topolski (now a renowned rowing journalist and broadcaster) as Chief Coach.

Part of the 1986/87 squad at Oxford included American Chris Clark, now a coach at an American University, and four fellow US internationals.

Allegedly, a split appeared in the squad between the American quintet, all experienced and leading oarsmen, and those rowers closest to Macdonald. The Scot’s group were happy to follow Topolski’s regime whilst the others were not so sure.

Following a contentious seat racing trial in January of 1987, Topolski decided to move Clark to the bow-side of the beat. Clark disagreed. Topolski held firm. As a result Clark and his "group" within the squad decided not to ROW and sought a takeover.

The squabble was played out extensively in the UK national media and caught the public imagination. MacDonald sought support from the college captains and eventually won a vote of confidence by 28 votes to 11.

Without the Americans, the Oxford crew was immediately considered a lost cause. Cambridge were overwhelming favorites to win.

As it turned out, though, this was a Race which would prove why sport, and particularly The Boat Race, can be so fascinating.

MacDonald had to seek support from the college captains because ().

A. the public imagined he was not competent to command his crew

B. the Chief Coach Topolski lost the experienced American oarsmen

C. the Oxford crew was unlikely to win the Race without the Americans

D. the Americans would leave the squad unless they were to lead it