Since the problem provides the information that the body is in motion, hence its speed is no longer zero, it experiences dynamic friction because static friction occurs when the speed of the body is equal to 0. The speed of a body in motion, along a surface, remains constant if the magnitude of applied force decreases, the moment the body starts to move.
The friction force may be evaluated using Coulomb's approximate model, such that:
F_f <= F_n*mu
mu represents the coefficient of friction
F_n represents the normal force, normal to the surface of friction between two bodies in contact
The coefficient of static friction mu_s is larger than the coefficient of dynamic friction, mu_k.