题目

人造地球卫星绕地球做匀速圆周运动，其轨道半径为r，线速度为ν，周期为T，若使卫星周期变为2T，使轨道半径变为r；使线速度变为v． 答案：考点：  向心力． 专题：  匀速圆周运动专题． 分析：  人造地球卫星绕地球做匀速圆周运动，由地球的万有引力提供向心力，牛顿第二定律推导周期T、线速度与半径的关系式，再进行解答即可． 解答：  解：设地球的质量为M，卫星的质量为m．由牛顿第二定律得：      G=m=m 得 T=2π；v= 据题，若There are many rules (制度) in the old libraries. For example, no photos, no drinking and no phones. But now a lot of libraries don’t have too many rules. They paint the rooms beautiful colors so readers would like to read there. There aren’t hard chairs in these libraries. There are nice sofas in them. Some of them are open 24 hours every day. In the libraries in America, readers can make a 1free call. That means that they don’t need to pay any money for making a call. In the kid’s library in Denmark, children can sleep there if it is too late. In some libraries in Australia, they have a kids’ “story time”. 2今天图书馆是孩子们娱乐和学习知识的好去处。任务（一）：根据短文内容回答下列问题。【小题1】Why do many libraries paint their rooms beautiful colors now? ________________________________________________________________________【小题2】In which country do some libraries have a kids’ “story time”? ________________________________________________________________________任务（二）：请写出1处下划线黑体单词“free”的汉语意思。【小题3】________________________________________________________________________任务（三）：请将文中2处划线的句子翻译成英语，每空一词。【小题4】Today libraries are good places for kids to ________ ________ and learn something.任务（四）：请给短文选择一个最恰当的英文标题。【小题5】A．New LibrariesB．Library RulesC．Old LibrariesD．Free Libraries