# Question #6624a

Jan 28, 2018
1. Total energy at the top of cliff

$m g h = 20000 J$
Inserting various values and taking $g = 10 m {s}^{-} 2$
$50 \times 10 \times h = 20000$
$\implies h = \frac{20000}{500} = 40 m$
(matches with the given number in the text.

2. Half way down $\frac{1}{2}$ of her energy has been converted in to her kinetic energy. If $v$ is her velocity half way down we get
$\frac{1}{2} m {v}^{2} = 10000$
$\implies {v}^{2} = 10000 \times \frac{2}{50} = 400$
$\implies v = \sqrt{400} = 20 {\text{ ms}}^{-} 1$