The height $($in feet$)$ of a stone dropped from a bridge $128$ feet above a river at $t=0$ seconds is given by $s(t)=-16t^2+128.$ Find the velocity of the stone and its speed when it hits the water

The velocity of the stone is

$($Type an exact answer, using radicals as needed.$)$

The speed of the stone is

$($Type an exact answer, using radicals as needed.$)$