Calculate the time it takes an object to reach the ground

Question

The height of a falling object is related to the time in seconds that the object has been falling by the formula h= -4.9^2+d where d is the initial height of the object above the ground. The Bankers Hall building in Calgary is 196m tall. Calculate the time an object takes to reach the ground from this height. Give your answer as an exact radical.

Answer 1

h(t)= -4.9t^2 +196= 0

t^2= 196/4.9 = 28/.7= 40

t=sqr40= 2sqr10 seconds to reach the ground