1. The problem statement, all variables and given/known data Let F , FN and f denote the magnitudes of the contact force , normal force and the force of friction exerted by one surface on the other kept in contact. If none of these is zero , then , (A.) F>FN (B.) F>f (C.) FN>f (D.) FN-f<F<FN+f 2. Relevant equations Well , I don't know whether object is moving with respect to other or not... In case of static friction , fs ≤ μsFN In case of kinetic friction , fk = μkFN < μsFN 3. The attempt at a solution http://postimage.org/image/yqh9rg6pl/ [Broken] OK , So obviously (A) is correct. (B) is also correct. (D) obviously is correct. (C) is also correct as it would mean that tanθ = μ <1 which is also true. So I go for A , B , C , D. But the textbook gives the answer A,B,D. Why is it so ? Where am I going wrong ?