A rock is thrown off a cliff. Its position vector r$$r$$ follows the path r$=(6$m$/$s$)$ti$^(4\mathrm{.}9$m$/$s$2)$t$2$j$^$r$=(6$m$/$s$)$ti$^(4\mathrm{.}9$m$/$s$2)$t$2$j$^.$ What is the horizontal velocity of the rock at any given time?

$6$ m$/$sm$/$s$0$ m$/$sm$/$s$-9\mathrm{.}8$ m$/$sm$/$sHorizontal velocity depends on time.