\(mg\,\,\left( {1.4} \right)\,\, = \,\,\frac{1}{2}\,\,m{v^2}\,\,\left( {1\,\, + \;\,\frac{{{K^2}}}{{{R^2}}}} \right)\)

\(\frac{{{K^2}}}{{{R^2}}}\,\, = \,\,\frac{2}{5}\,\) ઘન ગોળા માટે 

\(mg\,\,\left( {1.4} \right)\,\, = \,\,\frac{1}{2}\,\,m{v^2}\,\, \times \,\,\frac{7}{5}\)

\(v\,\, = \,\,\sqrt {20} \,\,\,\,\therefore \,\,\,\,R\,\, = \,\,u\,\,\sqrt {\frac{{2h}}{g}} \,\)

\(\,\therefore \,\,\,\,R\,\, = \,\,\sqrt {20} \,\,\sqrt {\frac{{2\,\, \times \,\,1}}{{10}}} \,\, = \,\,2\ m\)