[领域] (题目相关领域) 普物 [来源] (课本习题、考古题、参考书...) 考古题 [题目] A metal plate, mass M and length 2L, is on a table nearly cross to one table edge. A cubic steel block, mass M and side a (a < L), is put on the center of the metal plat. The distance of the center of the steel block from the table edge is d. Now we apply a force parallel to the table surface to pull the metal plate out successfully without any block falling to ground. What is the smallest force we need to apply? (Assume all the friction coefficients are μ) [瓶颈] (写写自己的想法，方便大家为你解答) 想用外力作功等於摩差力作功 可是又不知道摩差力怎样考虑 恳请板上高手指点 感谢 --

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