  In determining the mesonic wave function from QCD inspired potential model,
if the linear confinement term is taken as parent (with columbic term as
perturbation), Airy's function appears in the resultant wave function - which
is an infinite series. In the study of Isgur-Wise function (IWF) and its
derivatives with such a wave function, the infinite upper limit of integration
gives rise to divergence. In this paper, we have proposed some reasonable
cut-off values for the upper limit of such integrations and studied the
subsequent effect on the results. We also study the sensitivity of the order of
polynomial approximation of the infinite Airy series in calculating the
derivatives of IWF.
