Suppose you throw a rock off a cliff having height

$=1000$ feet. You're a strong bloke, so the initial downward velocity is

$=-100$ feet$/$sec $($slightly under $70$ miles$/$hr$).$ Further, in this neck of the woods, it turns out there is no friction in the atmosphere $-$ amazing! Now you remember from your Baby Physics class that the height after time

is h$($t$)=$ h$0+$ v$0$t $-16$t$^2$

When does the rock hit the ground?