题目内容
一重为P的小球在粗糙水平面内作纯滚动，当运动了一周时，重力、支承反力与摩擦力所做功都为零。
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Based on the different values in news, it can be categorized into hard news and soft news.
Based on different news media, it may include radio news, magazine coverage, newspaper coverage,TV news, mobile news, news on the internet.
News includes World news, home news and local news based on the location.
According to different contents of news, it may include Political news, Business news,Science and Technological news, Cultural news.
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