$\mathrm{Now}, T_{1}=\frac{A}{a} \sqrt{\frac{2}{g}[\sqrt{H}-\sqrt{\frac{H}{\eta}}]}$
and $T_{2}=\frac{A}{a} \sqrt{\frac{2}{g}}[\sqrt{\frac{H}{\eta}}-\sqrt{0}]$
According to problem $T_{1}=T_{2}$
$\therefore \operatorname{Sqrt}(H)-\sqrt{\frac{H}{\eta}}=\sqrt{\frac{H}{\eta}}-0 \Rightarrow \sqrt{H}=2 \sqrt{\frac{H}{\eta}} \Rightarrow \eta=4$


