问题 问答题

利用所学知识,推导第一宇宙速度的两种表达式v=

GM
R
v=
gR

答案

答:设地球半径为R,地球质量为M,卫星质量为m,

第一宇宙速度的轨道半径等于地球半径,

由牛顿第二定律得:G

Mm
R2
=
mv2
R

解得,第一宇宙速度v=

GM
R

在地球表面的物体受到的重力等于万有引力,

即:G

Mm′
R2
=m′g,则GM=gR2

则第一宇宙速度

gR

完形填空

阅读下文并回答问题。

Ben is now fifteen years old. He is interested in collecting coins. He has been collecting them for three years. He can still remember how he started to collect them.

Two years ago, on a Saturday morning, Ben was bored.  He didn’t have anything to do. He wasn’t interested in doing anything. He didn’t want to watch TV or listen to the radio. He didn’t want to play sports or read books. “I’m bored,” Ben said. “What can I do? I want to do something interesting.” Ben’s father had an idea. “I have an idea,” his father said. “Why don’t you collect coins? Coins are fun to collect. And coins are everywhere. You see coins every day. Some coins are valuable. They will make you rich.” Since then, he has been collecting them from his parents.

Now Ben has a big piggy bank (存钱罐) which is filled with coins. Sometimes he can take some of them to buy some snacks with his parents’ permission. In March, 2012, there was an earthquake in Yunnan, and Ben donated many of his coins to help the homeless children in Yunnan. He said he was happy to help others who are in trouble.

小题1:What is Ben interested in?

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小题2:Did Ben’s father advise Ben to collect coins?

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小题3:How did Ben feel when he helped others in trouble?

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