A tired and overloaded student is attempting to hold a large physics textbook we

Question

A tired and overloaded student is attempting to hold a large physics textbook wedged under his arm, as shown below. held in hand toward body

The textbook has a mass of 3.6 kg, while the coefficient of static friction of the textbook against the student's underarm is 0.320 and the coefficient of static friction of the book against the student's shirt is 0.160.
(a) What is the minimum horizontal force that the student must apply to the textbook to prevent it from falling?
N

(b) If the student can only exert a force of 64.1 N, what is the acceleration of the textbook as it slides from under his arm? The coefficient of kinetic friction of arm against textbook is 0.200, while that of shirt against textbook is 0.090.
magnitude m/s2
direction

Explanation / Answer

a) we can add the coefficients of static friction together, because there is only one force applied. so .480. Now the force of gravity on the book is mg, 3.6 x 9.8 = 35.28 N The force due to friction must be greater or equal to this 35.28 N force. so F(friction) = 35.28 = F x coef of friction F = 35.28 / .480 =73.5 N

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