问题 选择题

如图所示,某次发射远地圆轨道卫星时,先让卫星进入一个近地的圆轨道Ⅰ,在此轨道运行的卫星的轨道半径为、周期为;然后在P点点火加速,进入椭圆形转移轨道Ⅱ,在此轨道运行的卫星的周期为;到达远地点Q时再次点火加速,进入远地圆轨道Ⅲ,在此轨道运行的卫星的轨道半径为、周期为(轨道Ⅱ的近地点为Ⅰ上的P点,远地点为轨道Ⅲ上的Q点)。已知=2,则下列关系正确的是

A.

B.

C.

D.

答案

AC

由圆周运动周期公式=2,周期之比为,轨迹II和轨迹III可根据开普勒第三定律求解,,椭圆轨道的长半轴的长度为,可求出周期比值为,C对;

单项选择题
填空题


How many of us would temp for three years while we waited for the perfect job Not many of us, perhaps. But Wentworth Miller, the "Prison Break" star, said he chose to wait even longer time (1) he found the right job.
"Actually I think it might have been three or four years until I was lucky enough to get guest (2) on TV shows," said Miller, 34, who rose to international stardom (3) to "Prison Break" in 2006. That kind of patience and p will was portrayed in "Prison Break". Miller (4) engineering wizard Michael Scofield, who tries everything to break out of a Chicago (5) with his brother. Miller said he was fond of his character, (6) he said "exists in shades of grey".
Miller comes from a (7) of teachers. He said he didn’t seem fated for a career in the arts, (8) his passion for acting. After (9) from Princeton with an English degree, he moved (10) his parents’ request to Los Angeles to look for a stable life. He started (11) in a little company that made television movies. This (12) simply faxing, filing, walking the boss’ dog and going to the store for the boss’ lunch. Every weekend during the summer, Miller (13) go to the office (14) he didn’t have air-conditioning. "I would hang (15) in the conference room and set up camp and rob the company kitchen," recalled Miller.
(16) , Miller realized he still had questions about his choice. He decided to quit. But the boss said he was making a mistake and offered him a well-paid assistant position. "I eventually (17) that if I did the corporate job, it would be great if I was successful, but I would always wonder about the (18) . If I did the acting and was successful, I would never wonder (19) that job," he explained. He quit and temped (20) many people in the entertainment industry.
Now, he’s a hot star and has people coming up to him at film festivals saying, "Weren’t you the one who (21) to stand by the copy machine "
"That was tough, but I’m glad I have that perspective. Because now I’m at a point (22) big shots laugh at all my jokes and I think, You know, I got coffee for people like you for six years’. So I know what’s (23) , because I’ve seen the other side." But what if, when he was offered the corporate job, there had been more money "It was never about the (24) There’s a kind of excitement that comes along with acting. I can’t find it anywhere else. Even if I had to go back to temping, even if this is not the beginning of an amazing career, I would not (25) making that jum
p."