physics
posted by brian .
A student presses a book between his hands, as the drawing indicates. The forces that he exerts on the front and back covers of the book are perpendicular to the book and are horizontal. The book weighs 30.0 N. The coefficient of static friction between his hands and the book is 0.435. To keep the book from falling, what is the magnitude of the minimum pressing force that each hand must exert?

Each hand applies a maximum friction force
(0.435 F),
where F is the pressing force
Twice that force must equal or exceed the weight, M g
0.87 F > M g
Fmin = M*g/0.87 newtons