A warehouse worker is shoving boxes up a rough plank inclined at an angle B above the horizontal. The plank is partially covered with ice, with more ice near the bottom of the plank than near the top, so that the coefficient of friction increases with the distance x along the plank : mu=Ax, where A is a positive constant and the bottom of the plank is at x=0. (For this plank, the coefficients of kinetic and static friction are equal: mu(k)=mu(s)=mu.) The worker shoves the box up the plank so that it leaves the bottom of the plank moving at speed v0. Show that when the box first comes to rest, it will remain at rest if v02>or=(3gsin2B)/(AcosB) I drew a FBD and started the problem by solving for mgsinB = AxmgcosB. Basically that the friction was perfectly counteracted by that component of weight. => Ax=tanB I don't know where to go from here. I didn't know if I should use kinematics or energy or what?