Find the nodal displacements developed in the planar truss, when a vertically downward load of $1000$ N is applied at node $4.$ A$1=2$ cm $2,$ A$2=2$ cm $2,$ A$3=1$ cm $2,$ A$4=1$ cm $2,$ l$1=(2)50,$ l$2=(2)50,$ l$3=(2\mathrm{.}5)50,$ l$4=(2)100$ and constant E $=2\backslash$times $106$ N$/$cm$2$