Answer
(a) It takes $~~3.19~s~~$ to fall the first $50~m$
(b) It takes $~~1.33~s~~$ to fall the second $50~m$
Work Step by Step
(a) We can find the time it takes to fall $50~m$:
$y = \frac{1}{2}at^2$
$t = \sqrt{\frac{2y}{a}}$
$t = \sqrt{\frac{(2)(50~m)}{9.8~m/s^2}}$
$t = 3.19~s$
It takes $~~3.19~s~~$ to fall the first $50~m$
(b) We can find the total time it takes to fall $100~m$:
$y = \frac{1}{2}at^2$
$t = \sqrt{\frac{2y}{a}}$
$t = \sqrt{\frac{(2)(100~m)}{9.8~m/s^2}}$
$t = 4.52~s$
We can find the time it takes to fall the second $50~m$:
$4.52~s - 3.19~s = 1.33~s$
It takes $~~1.33~s~~$ to fall the second $50~m$.