  We study the ballistic adsorption of a polydisperse mixture of spheres onto a
line. Within a mean-field approximation, the problem can be analytically solved
by means of a kinetic equation for the gap distribution. In the mean-field
approach, the adsorbed substrate as approximated as composed by {\em effective}
particles with the {\em same} size, equal to the average diameter of the
spheres in the original mixture. The analytic solution in the case of binary
mixtures agrees quantitatively with direct Monte Carlo simulations of the
model, and qualitatively with previous simulations of a related model in $d=2$.
