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 30 kg. The coefficient of static friction betweent the covers and her hands is µs=0.49 and the coefficient of kinetic friction is µk=0.3.
c) 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?

Explanation / Answer

let's make h(height) = 1.2 m m(mass) = 30 kg µs=0.49 µk=0.3 c) the minum normal force required so that it does not slip from her hand could be used by the equation, you are right, you don't need to use the static or kinetice friction. You know that the normal force is equal to the gravitational force which is N = Fg Fg = mg. so N = mg N = (30)(9.8) N = 294 N

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