A metal bolt falls from a tower that is 68.6 meters high. As it is falling, its height h in meters at time t in seconds is given by the formula h=68.6 - 4.9t^2.

Question

How many seconds will it take for the bolt to hit the ground? 

Answer 1

Given h = 68.6 - 4.9t² and we want to solve for t when h = 0 we have

 

-4.9t² + 68.6 = 0

-4.9t² = -68.6

t² = (-68.6)/(-4.9)

t² = 14

t = sqrt(14) = 3.74 seconds

Answer 2

the height of an object on the ground is zero meters. Therefore if you set your formula 68.6-4.9t^2=0, you can find that at t=square root of 14, the object will be on the ground. That is approximately 3.4 seconds