\(\therefore \,\,{v_P} = \sqrt {Rg} \)
\(v_p^2 = v_L^2 - 2gR\) (\({v^2} = {u^2} - 2gh)\)
\({v_L} = \sqrt {v_P^2 + 2gR} = \sqrt {Rg + 2gR} = \sqrt {3gR} \)
\(k = \frac{1}{2}\,mv_L^2\)\( = \frac{1}{2}\,m\, \times 3gR\)
\(\frac{1}{2}k{x^2} = \frac{1}{2}\,3m \times \,g\,R\)
\(\therefore x = \sqrt {\frac{{3m\,g\,R}}{k}} \).