A student holds a physics book in her hands motionless 1.2 meter above the floor

Question

A student holds a physics book in her hands motionless 1.2 meter above the floor as shown to the left. The forces from her hands on the front and the back of the book are perpendicular to the book's cover and are horizontal. The mass of the book is 35 kg. The coefficient of static friction betweent the covers and her hands is s=0.44 and the coefficient of kinetic friction is k=0.32.

1)

What is the net force on the book in the x (horizontal) direction?

Fx =

Computed value:

2)What is the net force on the book in the y (vertical) direction?

Fy =

3) What is minimum normal force that the student can apply from each hand to the cover of the book to keep it from slipping through her hands?

Fmin =

Explanation / Answer

Since the book is motionless, net force in X and Y direction will be 0.

mg = 2x friction x force by each hand

consider kinetic friction which is 0.32, any force less than( 35 x 9.8) / (2 x 0.32) will let it slip (multiplied by 2 because we have to consider 2 normal forces acting due to 2 hands). Therefore, any force greater than 535.9375 will not let it slip.

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