Sir solve the first one
The system is pushed by the force F as shown in figure. All surfaces A B C are smooth except between B and C. Coefficient of friction between m B and C is μ. Minimum value of F to prevent block B from downwardNormal force between B and C is N
is given by N=2m×a
N=2F/5
B will not slide down if frictional force is more that the weight mg of block B
μN≥mg
F≥5mg/2μ
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