A small sphere of charge q1 = 0.768 C hangs from the end of a spring as in figure (a). When another small sphere of charge q2 = 0.

A small sphere of charge q1 = 0.768 µC hangs from the end of a spring as in figure (a). When another small sphere of chargeq2 = −0.648 µCis held beneath the first sphere as in figure (b), the spring stretches by d = 3.84 cm from its original length and reaches a new equilibrium position with a separation between the charges of r = 4.65 cm. What is the force constant of the spring?