You know the acceleration must be Zero in equillibrium.
I will just mark out the missing forces in your diagram. You can proceed with your mathematical working.
- Electrostatic Forces of the Charges over each other = Kliquid or mediumQ1Q2/R2. Directed to left for Q2 and to the right for Q1. K = 1/4(Pi)Eo(Di-electric constant).
- Buoyant Forces on the two masses due to liquid = (m/σ)ρg. Directed Upwards.
- NEGLECT Gravitational Forces between the two masses. It will just complicate the question needlessly.
- You must know that Di-electric constant of medium = Kvacuum or air / Kliquid or medium.
- You can find the state of the system OUTSIDE the liquid, or in air or vacuum. That is, the angle of string made with the vertical.
Theta is assumed to be GIVEN, alternatively you can calculate it.
This is all you need in addition to your current information to solve the question.
The rest is Forcenet = Mass x Acceleration = 0.
