a student presses a book between his hands. the forces that he exerts on the front and back covers of the book are perpendicular to the book and are...

a student presses a book between his hands. the forces that he exerts on the front and back covers of the book are perpendicular to the book and are horizontal. the book weights 31 N. the coefficient of static friction between his hands and the book is 0.40. to keep the book from falling, what is the magnitude of the minimum pressing force that each hand must exert?