  Variational study of $_\Lambda ^5$He hypernucleus is presented using a
realistic Hamiltonian and a fully correlated wave function including $\Lambda
N$ space-exchange correlation. Behaviour of the $\Lambda$-separation energy
($B_\Lambda$) with two- and three- baryon potential strengths is thoroughly
investigated. Solutions of the potential strengths giving experimental
$B_\Lambda$ are presented.
