Answer:
D) 14 seconds
Step-by-step explanation:
y = -4.9t^2 + 120t
We want to find out when y = 500
500 = -4.9t^2 + 120t
Subtract 500 from each side
500-500 = -4.9t^2 + 120t-500
0 = -4.9t^2 + 120t-500
a=-4.9 b= 120 and c = -500
Using the quadratic formula
-b ±sqrt(b^2 -4ac)
-------------------------
2a
-120±sqrt(120^2 -4(-4.9)(-500))
-------------------------
2*(-4.9)
Solving this for the two solutions
t≈5.32415
t≈19.1656
The object will be above 500 meters between these two times
19.1656 - 5.32415 = 13.84145
This is approximately 14 seconds
