A roller coaster starts from rest at its highest point and then descends on its $($frictionless$)$ track. Its speed is $24$ m$/$sm$/$s when it reaches ground level.

Part A

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

$12$ m$/$sm$/$s$8\mathrm{.}5$ m$/$sm$/$s$20$ m$/$sm$/$s$17$ m$/$sm$/$s