\[h = \frac{gt^{2}}{2};\ \ \ g \approx 10\ \frac{м}{с^{2}};\ \ \]
\[h = 120\ м.\]
\[t^{2} = \frac{2h}{g}\]
\[t = \sqrt{\frac{2h}{g}} = \sqrt{\frac{2 \cdot 120}{10}} = \sqrt{24} =\]
\[= 2\sqrt{6} \approx 2 \cdot 2,5 \approx 5\ с.\]
\[Ответ:примерно\ 5\ с.\]