  Accurate massloss rate estimates are crucial keys to study wind properties of
massive stars and test different evolutionary scenarios. From a theoretical
point of view, this implies to solve a complex set of differential equations in
which the radiation field and the hydrodynamics are strong coupled. The use of
analytical expression to represent the radiation force and the solution of the
equation of motion have many advantages over numerical integrations. Therefore,
in this work, we present an analytical expression as solution of the equation
of motion for radiation driven winds, in terms of the force multipliers
parameters. This analytical expression is obtained by employing the line
acceleration expression given by Villata (1992) and the methodology proposed by
Mueller and Vink (2008). On the other hand, we find useful relationships to
determine the parameters for the line acceleration given by Mueller and Vink
(2008) in terms of the force multiplier parameters.
