Thread: physics w/ Forces

a person 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.

Now the book weighs 40 N.

The coefficient of static friction between his hands and the book is 0.31

To keep the book from falling, what is the magnitude of the minimum pressing force that each hand must exert?

In Newtons.

- Friction acts perpendicular to the normal force.


- To prevent falling the frictional force must be at least equal and opposite to the weight force.

μ = 0.31


Friction = 0.31 * F

0.31*F ≥ 40


F ≥ 40/0.31


F ≥ 129 N

Each hand must exert ½ * 129 N to prevent the book from falling.