Posted by Syed on .
A rock is dropped from the top of a 400foottall building. Its distance s (in feet) from the top of the building after t seconds is s(t) = 16t^2. How many seconds will it take the rock to hit the ground?

Calculus 
Steve,
hit the ground == drop 400 ft. So,
16t^2 = 400
Now just solve for t.