如图所示，光滑的水平面上有一个质量为M=2m的凸型滑块，它的一个侧面是与水平面相切的光滑曲面，滑块的高度为h=0.3m．质量为m的小球，以水平速度v0在水平面上迎着光滑曲面冲向滑块．试分析计算v0应满足什么条件小球才能越过滑块．（取g=1Om/S2）
设小球越过滑块最高点的速度为v1，此时滑块的速度为v2，根据动量守恒得：
mv0=mv1+2mv2
此过程系统机械能守恒，根据机械能守恒得：
mv02=1 2
mv12+1 2
2mv22+mgh1 2
小球要越过滑块，应有v1＞v2，至少也要有v1=v2，设v1=v2=v，上述两式变为
mv0=（m+2m）v
mv02＞1 2
（m+2m）v2+mgh1 2
解得v0＞3m/s
答：小球要越过滑块，初速度应满足v0＞3m/s．
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| When describing people, we often use the three common words: men, women, children. ___1_ of us agree that boys and girls should have __2__ rights. But in almost every society in the __3__, girls are treated less well than boys. __4__, people paid little attention to differences __5__ boys and girls and the ways in _6__ they were treated. However, recent research __7__ that girls receive less attention than boys in matter __8__ as schooling, health, jobs and earnings. __9__ girls were valued and treated as well as boys, there would be _10__ another 100 million women in the world. In___11_ countries of the world, girls live with families __12__ whom they work as servants. They _13___ twelve hours a day, often receive no__14__, have no bedroom of their own and are not __15__ to run away. Why doe this happen? The __16__ is that poor families who live in the country __17__ not be able to have enough food for all their children. So girls are ___18___ to families in towns to work __19__ servants. In Haiti there are 109,000 children, __20__ girls, aged 5-18 who live with rich families and work for nothing. | ||||
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