A boy pulls a wooden box along a rough horizontal floor at constant speed by means of a force P as shown. In the diagram, f is the magnitude of the force of friction, N is the magnitude of the normal force, and Fg is the magnitude of the force of gravity.

Which of the following must be true? P = f and N = Fg, P > f and N < Fg, P > f and N = Fg the object must come to rest and remain at rest, P = f and N > Fg