Two balls have the same mass of 3.085 kg and identical charges of 21.0 ìC. They hang from the ceiling on strings of identical length as shown in the figure. If the angle with respect to the vertical of the strings is 22.0°, what is the length of the strings

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  1. Are the two strings attached to the same point on the ceiling? If so, consider the net torque on either ball about the ceiling attach point. it must be zero.

    The gravity (weight) torque balances the Coulomb-force torque.
    M*g*Lsin22 = k q^2*Lcos22/(2Lsin22)^2

    L can be solved for. Everything else is known

    L^2 = (1/4)[k q^2/(Mg)]*cos22/(sin22)^3

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