There is a wood block with mass m on the board with mass M. the dynamic friction factor between the board and the wood block is μ 1 The dynamic friction factor between the board and the horizontal ground is μ 2. What is the force F on the board before the board can be pulled out from under the board?
The sliding friction on the upper surface of the board is μ 1mg, and that on the lower surface is μ 2 (M + m) g
Therefore, it is necessary to pull out the board at least f = μ 1mg + μ 2 (M + m) g
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