Question

V0=0
h=78м

t-?
g=9.8 м/c2

Answer 1

$h \: = \frac{g {t}^{2}} {2}$
$t \: = \: \sqrt{ \frac{2h}{g} }$
$t \: = \: \sqrt{ \frac{2 \times 78}{9.8} }с ≈ 4$с