We have investigated the random walk problem in a finite system and studied
the crossover induced in the the persistence probability scales by the system
size.Analytical and numerical work show that the scaling function is an
exponentially decaying function.The particle here is trapped with in a box of
size L . We have also considered the problem when the particle in trapped in
a potential. Direct calculation and numerical result show that the scaling
function here also an exponentially decaying function. We also present
numerical works on harmonically trapped randomly accelerated particle and
randomly accelerated particle with viscous drag.Comment: revtex4, 4 pages, 4 figure