Are electric force and strong force equal in magnitude? Should the electric force and the strong force be equal for a nuclei to be stable? Because if perhaps, the strong force is now more than that of the electric force, then shouldn't the nucleus collapse due to the constant interaction of the particles in the nucleus?
 A: There is a repulsive force that comes into play whenever you try and confine particles to a restricted area. It is this repulsive force that stops the nucleus contracting to a point.
Whenever you have a bound state of particles you get discrete energy levels. This applies to the electron in a hydrogen atom, where we get the $1s$, $2s$, etc states, and it applies also to the quarks inside a proton or neutron. In such systems the ground state does not have zero energy but instead has a non-zero energy called the zero point energy. This zero point energy is inversely related to the size of the bound state. If we make the bound state smaller the zero point energy goes up, and if we make it larger the zero point energy goes down. This results in a repulsive force because in general systems want to lower their energy and the bound state lowers its energy by expanding outwards.
To start with a simple system consider a hydrogen atom. The electrostatic attraction between the proton and electron wants to pull the two together, but this decreases the size of the atom and as a result the zero point energy increases. The observed size of the hydrogen atom is the size where these two opposing effects balance out, and that's why the hydrogen atom doesn't shrink to a point.
And the same applies to the protons and neutrons in a nucleus. The strong force does pull the quarks together, but the zero point energy opposes this attractive force, and we end up with the two effects balancing out at the one femtometre size we observe for protons and neutrons.
The point of this is that it isn't the electrostatic force that stops the proton or neutron collapsing, it's the zero point energy. So there is no requirement for the electrostatic and strong forces to be in equilibrium, and indeed they aren't.
