Question

A rock breaks loose from a cliff and plunges toward the ground 400 feet below. The distance "d" that the rock falls in "t" seconds is given by the equation d=16t^2. How long does it take the rock to hit the ground?

Answer 1

the distance the rock has to travel to hit the ground is 400ft.  
400 = 16 * t^2divide both sides by 16 and take the square root.  
25=t^2

5=t