A particle A has charge q anda particleB has charge 4q with each of them having same mass m. when allowed to fall from rest through sam potential difference , the ratio of their speed va:vb will be:

Particle A has:Charge = q, Mass = m, Potential = V 

Particle B has:Charge = 4q,Mass = m,Potential = V

Now using,Kinetic energy, K = work done by charge = charge x potential

And kinetic energy = 

Using above two formulas of kinetic energy