
In upward moving lift $T' = 2\pi \sqrt {\frac{l}{{(g + a)}}} $ ($a = $Acceleration of lift)
$ \Rightarrow \frac{{T'}}{T} = \sqrt {\frac{g}{{g + a}}} = \sqrt {\frac{g}{{\left( {g + \frac{g}{4}} \right)}}} = \sqrt {\frac{4}{5}} $
$ \Rightarrow T' = \frac{{2T}}{{\sqrt 5 }}$


