Question

A block of wood is pulled by a horizontal string across a horizontal surface at constant velocity with a force of 74 N. The coefficient of kinetic friction between the surfaces is 0.2. What is the magnitude of the force of friction?

Answer 1

Constant velocity means Σa_{x}=0, thus ΣF_{x}=0. The forces acting on the block are 74+f_{k,x}=ΣF_{x}=0, where f_{k,x}=-74N.