500
In order to shove a rock out of the way, the gardener gets it moving by exerting just slightly more than 100 Newtons of force. To keep it moving at a constant velocity eastward, however, the gardener needs only to exert a 45-Newton force to the east. What is the KINETIC frictional force between the rock and the ground?
What is 45 Newtons--enough force to overcome the kinetic frictional force, but no more; acceleration is zero.