6. An electric dipole consists of two equal and opposite charges (+q) separated by a distance d. Find the approximate electric potential at point P. (d ＜＜ r)Ans：___(9)____

(a).Suppose that the cylinder is sliding without rolling down the smooth inclined face of the wedge, and the wedge is free to move on a horizontal plane with friction. How far has the wedge moved by the time the cylinder has descended from a rest a vertical distance h?Ans：___(1)____