A roller coaster starts from rest at its highest point and then descends on its $($frictionless$)$ track. Its speed is $28\frac{m}{s}$ when it reaches ground level.

Part A

What was its speed when its height was half that of its starting point?

$14\frac{m}{s}$

$23\frac{m}{s}$

$20\frac{m}{s}$

$9\mathrm{.}9\frac{m}{s}$