题干

如图所示,B、C、D、E、F,5个小球并排放置在光滑的水平面上,B、C、D、E,4个球质量相等,而F球质量小于B球质量,A球的质量等于F球质量.A球以速度v0向B球运动,所发生的碰撞均为弹性碰撞,则碰撞之后(   )

A:5个小球静止,1个小球运动

B:4个小球静止,2个小球运动

C:3个小球静止,3个小球运动

D:6个小球都运动

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C

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    It's time to stop complaining. The economy might be melting down like butter in a hot pot, but for some people — you , maybe? — this could be a very good thing.

    Here's why. At no other time in recent history has it been easier or cheaper to start a new kind of company. Possibly a very profitable company. Let's call these start-ups LILOs, for “a little in, a lot out;” These are Web-based businesses that cost almost nothing to get off the ground yet can turn into great moneymakers.

    How do you get started? All that's required is a great idea for a product that will fill a need in the 21st century. These days you'd do best if your idea either makes people money or saves them money. And launching now will make your company stronger later — you'll learn to survive on fumes until the economy improves.

    That's what John Tayman is doing. He's an author who lives in San Francisco, where I met him; he wrote reviews for a business magazine I edited. Tayman knew little about technology and even less about business. And yet he dreamed of a website that would summarize car reviews from other sources and rank every model of new car. “It'll be like RottenTomatoes.com meets Kelley Blue Book,” he explained to me during lunch one day last June. Tayman said he intended to build the site on the side while continuing to write for a living. He'd work on his new company only at night and on weekends. Oh, yes, and he had only about $10,000. “Good luck with that!” I thought. Ideas are much easier to produce than they are to put into practice.

    Tayman went to work with nothing more than his PowerBook laptop. A very well-organized fellow, he quickly discovered a bunch of free stuff online — instructional manuals and sites that walk you through the process from start to finish. Within months, Tayman had a staff of 20 employees working for him in five different countries. MotorMouths.com went live in January. Tayman figures he has worked about 10 hours a week on it and hasn't spent a cent on marketing or advertising. Growth is modest but steady: nearly 10,000 people visit each week.