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 39 kg. The coefficient of static friction betweent the covers and her hands is ?s=0.4 and the coefficient of kinetic friction is ?k=0.32.

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

?Fy =

N

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

2. Since the object is motionless, Net Force along Y Direction = 0 Answer

3. Due to applied Force on each hand, static friction will develop upwards on the book, from both hands to balance the weight of the book,

therefore, 2 x us x Fmin = mg

Fmin = mg / 2us = (39 x 9.8) / (2x0.4) = 477.75 N Answer

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