A Boy Pulls a Wooden Box Along a Rough Horizontal

Multiple Choice

A boy pulls a wooden box along a rough horizontal floor at constant speed by means of a force as shown. In the diagram f is the magnitude of the force of friction, N is the magnitude of the normal force, and F_g is the magnitude of the force of gravity. Which of the following must be true?

A) P = f and N = F_g
B) P = f and N > F_g
C) P > f and N < F_g
D) P > f and N = F_g
E) none of these