题目

如图物块重为20N，放在倾斜角为37°的斜面上，求物块对斜面的压力和摩擦力． 答案：考点：  物体的弹性和弹力． 专题：  共点力作用下物体平衡专题． 分析：  以物块为研究对象，分析受力情况，根据平衡条件求解斜面对物块的摩擦力和支持力． 解答：  解：对物体受力分析，受竖直向下的重力mg，平行于斜面向上的摩擦力f，和垂直于斜面向上的支持力N， 正交分解可得：平行斜 For many kids in Africa， the colorful PlayPump(踏水车）is the first playground thing they have ever seen. When the children give it a push and jump in for their first ride， smiles of wonder appears on their faces.The fun of going round and round in a circle is just part of the wonder. The wonderful invention doesn’t only change the kids’ play time， but also makes a big difference to the people’s lives.As the merry-go-round starts， it pumps(泵送）clean water up from deep underground and keeps it in a huge tank(桶）. People are welcomed to come and help themselves to get the water for free. They are very happy these days.In the countryside of Africa， very few people could drink clean water. They don’t have machines that can get water in their homes. Instead， they often walk a long way to carry water back.Patricia Molope， a fifteen-year-old girl， explains that before her village in South Africa got a PlayPump， people would pay a taxi driver to take them to a well far from their homes. “ Sometimes the taxi drivers were so busy that we would have to stop taking showers in order to save water. It was so far to walk there， but at present we have our own clean water in the village， and the life is better， too.”The hard job of carrying water usually is done by women and girls. Carrying water for miles and hours each day is such a heavy job that it sometimes prevents girls from being able to go to school.Thanks to the PlayPump， getting water is quicker and easier-----and even boys join in. The pumps have become a new activity. Kids and adults seem to love playing with them while collecting water.A boy named Khumalo， twelve years old， says， “ I have seen many kinds of water pumps， but have never seen one that can keep water. When I grow up， I want to be an inventor so I can also invent clever things like the PlayPump that will help my country.”So far， more than 800 PlayPumps are being operated in schools and neighborhoods in four African countries， providing water for almost two million people.1.To get water from a PlayPump， people need to ______________.A. walk for a long way B. push it firstC. make it in a circle D. use a big tank2.The underlined word “it” in Paragraph 3 refers to____________A. pump B. merry-go-roundC. PlayPump D. underground3.For Patricia Molope， getting water used to be hard because____________A. She didn’t know how to use a PlayPump.B. She had no money to pay a taxi driver.C. The only place to get water was far away from home.D. There was not enough water in the well.4.Which of the following is NOT TRUE about PlayPump?A. People need to pay for the clean water from PlayPump.B. Both children and parents enjoy the ride on PlayPump.C. PlayPump makes the life of the Africans much easier.D. About two million Africans are using the water from PlayPump.5.What is the main idea of the story?A. PlayPump can bring people together.B. PlayPump helps turn work into play.C. Every country in the world is thirsty.D. PlayPump is a great invention in the world.