A book of mass M is positioned against a vertical wall. The coefficient of friction between the book and the wall is μ. You wish to keep the book from falling by pushing on it with a force F applied at an angle θ with respect to the horizontal (−π/2 < θ < π/2), as shown in the figure. (a) For a given θ, what is the minimum F required? (b) For what θ is this minimum F the smallest? What is the corresponding minimum F? Answers a) Fmin = Mg μscosθ+sinθ b) θ = tan−1 1/μs, Fmin = Mg μs2+1