Chapter 17, Problem 12P

** Tow objects with charges q and 4q are separated by 1.0 m. (a) Determine the charge (both sign and magnitude) and position of a third object that causes all three objects to remain in equilibrium (all three objects are on the same line). (b) Is the equilibrium stable or unstable? How do you know? (Hint: An object is in a stable equilibrium if a small displacement of the object from the equilibrium results in a force exerted on the object that points opposite to the direction of displacement.)