## Physics: Principles with Applications (7th Edition)

a) The free-body diagram shows the box at rest on a inclined plane. The $F_{fr}$ is Static Frictional Force since the box is at rest. b) If the box were sliding down the plane, the free-body diagram will be unchanged but $F_{fr}$ will be the Kinetic Frictional Force since the box is moving down the plane. c) If the box were sliding up the plane, the free-body diagram will be unchanged but $F_{fr}$ will be the Kinetic Frictional Force and arrow pointing in the opposite direction since the box is moving up the plane.