质量分别为m、2m、3m的物块A、B、C叠放在光滑的水平地面上,现对B施加一水平力F,已知AB间、BC间最大静摩擦力均为f0,为保证它们能够一起运动,F最大值为（ ）
A．6f0 B．4f0 C．3f0 D．2f0
答案：D
题目分析：先对A、B、C整体分析，受重力、支持力和推力，根据牛顿第二定律，有
，若AB恰好相对静止，则
，此时
，若C和AB恰好相对静止则
，此时
，为了保证ABC能够一起运动，则应满足
。
故选D
点评：此类问题应找到刚好三个物体没有相对运动时哪个面到达最大静摩擦力。
| 阅读理解。 | ||||
| An old farmer lived with his grandson. Each morning, the 1 got up early and read his Bhagavad Gita (薄迦梵歌). One day the grandson asked, "Grandpa! I try to read the book like you 2 I can't understand it, and I forget it easily. What's the 3 of reading it?" The grandfather said, "Take this coal (煤炭) basket down to the 4 and bring me back a basket of water." The boy did as his grandfather 5 , but all the water ran 6 he got home. The grandfather laughed, "You'll have to move faster next time." This time the boy 7 faster, but again the basket was empty. He told his grandfather that is was 8 to carry water in a basket. He wanted to use a bottle instead, but the old man said, "I just want a basket of water. You're not 9 hard enough." The boy wanted to show his grandfather that the water would surely run. He again put the 10 into the river and ran hard. But there wasn't anything in it again. He said 11 ,"Look, grandpa, it's useless!" "Watch the basket." said the grandfather. For the first time the boy 12 the basket was different. It had changed from a dirty old coal basket into a 13 one, inside and out. "Boy, you might not understand or remember 14 when you read the book, but when you read it, you will be 15 , inside and out. That's what you got from it." | ||||
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