Question

The angle between the resultant contact force and the normal force exerted by a body on the other is called the angle of friction. Show that if λ be the angle of friction and µ the coefficient of static friction, λ≤ tan-1µ . Concept of Physics - 1 , HC VERMA , Chapter 6:Friction "

Answer 1

Solution :
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let F be the applied force
R be the frictional force'
R be the normal force
u= tan λ=F/R
When F =μR 
F is the limiting friction .
when applied force increases , force of friction increases upto limiting friction.
Before reaching limiting friction :
F <μR/F
tanλ=F/R < μR
tan λ≤ μ
λ≤ tan⁻¹μ