How fast does it take the rock to hit the ground?

Question

A rock breaks loose from a cliff and plunges toward the ground 400 feet below. The distance d that the rock falls it t seconds is given by the equation d=16t². How long does it take the rock to hit the ground?

Answer 1

400 = 16t²

t² = 25

t = 5

 

It takes 5 seconds for the rock to hit the ground.