(1) The car accelerates (its speed decreases) because a horizontal frictional force acts against the motion, in the negativedirection of the x axis. (2) The frictional force is a kinetic frictional force with a magnitude given by Eq. 6-2 ( fk mkFN), inwhich FN is the magnitude of the normal force on the car fromthe road. (3) We can relate the frictional force to the resultingacceleration by writing Newton’s second law (Fnet,x max) formotion along the road.