2007年10月24日，我国成功地发射了“嫦娥一号”探月卫星。卫星进入地球轨道后还需要对卫星进行10次点火控制。前4次点火，让卫星不断变轨加速，当卫星加速到
的速度时进入地月转移轨道向月球飞去。后6次点火的主要作用是修正飞行方向和被月球捕获时的紧急刹车，最终把卫星送入离月面h=200km高的工作轨道（可视为匀速圆周运动）。已知地球质量是月球质量的81倍，
，卫星质量为2350kg，地球表面重力加速度
，引力恒量
。(结果保留一位有效数字）求：
(1)地球的质量。
(2)卫星从离开地球轨道进入地月转移轨道最终稳定在离月球表面h=200km的工作轨道上外力对它做了多少功？（忽略地球自转及月球绕地球公转的影响）
(1) 
(2) 
题目分析：（1）根据
，解得
；
（2）设卫星离月球200km轨道时的速度为v，由牛顿定律可知：
，而
对卫星由动能定理可得 
.
| 完形填空。 | ||||
| In May, 1927, at least four different people were planning to fly between New York and Paris. On the morning of. May 20, however, only Lindbergh 1 from New York in his small plane. For the first eleven hours he flew 2 the Atlantic coastline (海岸线). When he turned groud the open ocean, he had flown almost as far and as long as Al cock and Brown had in 1919. It was getting dark and the 3 part of the flight was just beginning. First, there was freezing fog (冻雾). For a time he avoided (避免) this by flying low over the water. But then the fog 4 down to the tops of the waves. Lindbergh. flew 5 but it was so 6 that ice formed on his wings (机翼) In the black darkness he shook the ice off 7 diving and turning sharply. Twenty-four hours had passed now and he was terribly 8 . He was still over the At lantic in darkness. He ate 9 because he thought it would be easier to stay awake on an empty stomach (胃). Then dawn, (黎明) came. A few minutes later, he was over the Irish coast. He flew on over England and crossed France. Ahuge, excited crowd of 1"00,000 people were waiting for him when he 10 . He had flown for thirty-three and a half hours. It is probably one of the most famous flights in history. | ||||
|