Numerical

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Draw the forces on the charges when they are in air. These will be the weight, the tension in the string and the repulsive force between the spheres. Put the net force equal to zero if the spheres are in equilibrium in this situation. For this equate the forces along the x axis to zero and those along the y axis to zero.

Next for the spheres immersed in the liquid, consider the weight, the buoyant force, the repulsive force and the tension in the string. Put the net force equal to zero.

Write the equations for the 2 cases and solve them. In case of any difficulty please let me know.