Answer:
B. 4.3 seconds
Explanation:
Given: The height above ground after t seconds is given by the equation h=-16t^2+400 where h is the height of the jumper in feet and t is the time in seconds since her jump.
To find time to reach the height (h) = 100 ft above the ground, we need to plug h = 100 in the given equation and solve for t.
100 = -16t^2 + 400
Subtract 400 from both sides, we get
100 - 400 = -16t^2 + 400 - 400
-300 = -16t^2
Now divide both sides by -16, we get
-300/-16 = -16t^2/-16
t^2 = 18.75
Now take square root on both sides.
√t^2 = √18.75
t = 4.3 seconds.