A48.1-kg crate rests on a level floor at a shipping dock. The coefficients of static and kinetic friction are0.570and0.388, respectively. What horizontal pushing force is required to (a) just start the crate moving and (b) slide the crate across the dock at a constant speed?

In order to start the crate moving, the magnitude of the horizontal force must be at least as large as the maximum static frictional forcefsMAX=sFN. When the crate is moving at constant velocity, the net force on the crate is zero. Thus, the horizontal force must be equal to the kinetic frictional force.