A rough vertical board has an acceleration a so that a 2kg block pressing against it does not fall. The coefficient of friction between the block and the board is μ. Then,
A
μ>ga
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B
μ<ga
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C
μ<ag
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D
μ>ag
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Solution
The correct option is Aμ>ga The FBD of the block is shown below in the board frame of reference.
From the FBD, we get N=ma and f=μN=μma (in limiting case) If block does not fall, it means f>mg ⇒μ(ma)>mg ⇒μ>ga