The book's position is changing linearly with time, so its velocity is constant. This means that the net force acting on the book in the direction <u>parallel</u> to the surface is
∑ <em>F</em> = 10.0 N - <em>n</em> = 0
where <em>n</em> is the magnitude of the normal force on the book due to the wall, and the net force perpedicular to the surface is
∑ <em>F</em> = <em>f</em> - (0.550 kg) <em>g</em> = 0
where <em>f</em> is the mag. of kinetic friction, and <em>f</em> = <em>µn</em> where <em>µ</em> is the coefficient of kinetic friction.
Then
• <em>n</em> = 10.0 N
• <em>f</em> = (0.550 kg) <em>g</em> = 5.39 N
• 5.39 N = <em>µ</em> (10.0 N)
==> <em>µ</em> = 0.539