Question

The function y = -16t 2 + 486 models the height y in feet of a stone t seconds after it is dropped from the edge of a vertical cliff. How long will it take the stone to hit the ground? Round to the nearest hundredth of a second. A. 5.51 seconds B. 0.25 seconds C. 7.79 seconds D. 11.02 seconds

Answer 1

that is when the height is 0
0=-16t^2+486
solve
add 16t^2 to both sides
16t^2=486
divide both sides by 16
t^2=243/8
sqrt both sides
t=5.511
round
t=5.51 seconds

answer is A