Two 0.10-g pith balls are suspended from the same point by threads 30 cm long. (Pith is

Question:

Two 0.10-g pith balls are suspended from the same point by threads 30 cm long. (Pith is a light insulating material once used to make helmets worn in tropical climates.) When the balls are given equal charges, they come to rest 18 cm apart, as shown in Fig. 15.28. What is the magnitude of the charge on each ball? (Neglect the mass of the thread.)