STANDARD Physics Friction MCQ Question
A block of mass M is held against a rough vertical wall by pressing it with a finger. If the coefficient of friction between the block and the wall is μ and the acceleration due to gravity is g, what is the minimum force required to be applied by the finger to hold the block against the wall?
μMg
Mg
Mg/μ
2μMg
Correct Answer
Detailed Explanation
Let F be the force applied by the finger on the block. N is the normal reaction of the wall on the block. Mg is the weight of the block acting vertically downwards. f is the force of friction between the wall and the block which acts upwards. The block will not fall if f = Mg. Since f = μN and N = F, we have μF = Mg, thus F = Mg/μ.
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