#### Answer

(a) The tower should be 78.4 meters high.
(b) The impact velocity is 39.2 m/s

#### Work Step by Step

(a) $y = \frac{1}{2}at^2$
$y = \frac{1}{2}(9.80~m/s^2)(4.0~s)^2$
$y = 78.4~m$
The tower should be 78.4 meters high.
(b) $v = v_0+at = 0 + at$
$v = (9.80~m/s^2)(4.0~s)$
$v = 39.2~m/s$
The impact velocity is 39.2 m/s