Question

Two tiny spheres of mass m = 7.80{\rm mg} carry charges of equal magnitude, 72.0 {\rm nC}, but opposite sign. They are tied to the same ceiling hook by light strings of length 0.530 {\rm m}. When a horizontal uniform electric field E that is directed to the left is turned on, the spheres hang at rest with the angle \theta between the strings equal to 50.0^{\circ} in the following