1. The problem statement, all variables and given/known data A boy supports a book on his hand while standing still. Then, he walks with the book laying motionless on his hand. Is there work exerted by the boy on the book? 2. The attempt at a solution My professor said that there is zero work done on the book because of the perpendicularity of the displacement of the book and the force applied by the boy on the book. But, I ask, if the book moved from rest, doesn't it mean it accelerated? If it accelerated, doesn't it mean that a net force along the x-axis acted on it? If so, then doesn't it mean that there IS work? Please help.