One icy day, my brother Nate decides to load boxes into his commissary truck by sliding them up a ramp into the back of his truck. The ramp makes an angle ? with the horizontal, and is only partially covered in ice, such that the coefficient of friction, ? increases as you go up the ramp as ?k = ?s = ? = Dx, where D is some positive constant, and x = 0 corresponds to the bottom of the ramp. If Nate initially pushes the box up the ramp at velocity v0, find the minimum velocity necessary such that when the box comes to rest it will stay at rest.