A body of mass M is kept on a rough horizontal surface (friction coefficient = μ). A person is trying to pull the body by applying a horizontal force but the body is not moving. The force by the surface on A is F, where
Mg F Mg
If F1 = 0
So contact force will only have Normal which is equal to Mg
So F will be Mg
Now as F1 increases fr keeps increasing till it reaches limiting value i.e., μN = μ mg
So in that case contact force F will be
√N2+fr2 = √(Mg)2+(μMg)2
F = Mg √1+μ2
This means contact force F will lie between Mg ≤ F ≤ Mg √1+μ2