阅读下面短文，根据短文内容回答问题。
What is the hottest topic at your school? In Hangzhou Yongjin Middle School, it's money.
The school ran an activity called "Making a Living" recently. About 800 Junior One and Junior
Two students were divided into teams. They went out to make money by selling things.
What did they choose to sell? Some sold newspapers, some sold bottled water, some sold
shopping bags and bamboo baskets. They sold different kinds of things.
Hu Qi's team decided to sell educational books in front of the. Children's Center.They thought
parents would like to buy books for their children. But unfortunately, they came across urban
management officers.The officers asked them to leave. "We played hide-and-seek (捉迷藏) with the
officers the whole morning," said Hu."Finally we gave up and moved to another place. "
Wang Yongyi and her team sold ice creams in a square. They didn't meet any officers. But few
people were interested in what they were selling. The team then set a board saying the money was to
help the kids in the country. It worked. More people came to their stall (小摊). A foreigner even
gave them 100 yuan. He said he wanted to help the children.
Meng Zhaoxiang and his team were luckier. They sold all their cakes in four hours, spending 39. 5
yuan and getting back 80 yuan. They made 40.5 yuan. "It was not easy to make the money," said
Meng. "Some people just looked. Others just tasted but didn't buy. " "Now, we know how hard it
is for our parents to make money," said the students.
1. Is the name of the activity "Making a Living"?
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2. Why did the students in Hu Qi's team choose to sell books?
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3. What will Wang Yongyi's team use the money to do?
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4. How many teams are mentioned in the article?
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5. What's the purpose of the activity?
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，mg的大小为滑块所受合力，则测出滑块下落的距离x，合外力对滑块做功的表达式为mgx.
，得到：M=2/k.