અંદાજે \(D\) અચળ છે અને \( I = (L/r^{2})\)
\(\frac{{{L_1}}}{{r_1^2}}\,\, \times \,\,{t_1}\,\, = \,\,\frac{{{L_2}}}{{r_2^2}}\,\, \times \,\,{t_2}\,\,\, \)
\(\Rightarrow \,\,\,\,\,\frac{{40}}{{{{(0.6)}^2}}}\,\, \times \,\,20\,\,\, = \,\,\frac{{20}}{{{{(1.2)}^2}}}\,\,t\,\,\)
\( \Rightarrow \,\,\,t\,\, = \,\,160\,\,s\)