117k views
0 votes
Jeongin kicks a stone off the edge of a tall cliff. The distance, d, between the rock and the ground t seconds after being kicked is d = -16t² -6t +480. How many seconds go by before the rock is at height of 424 feet above the ground?

mkay so I tried to solve it, but the factoring seems really off when I tried to find t. Is it really solvable or am I missing something? help would be appreciated thank youu :)​

User Judyann
by
6.8k points

1 Answer

0 votes

Answer:

  • 1.693 seconds

Explanation:

Given function

  • d(t) = -16t² -6t +480
  • Find t, when d = 424

Solution

  • -16t² -6t +480 = 424
  • -16t² -6t +480 - 424 = 0
  • -16t² -6t + 56 = 0
  • 8t² +3 t - 28= 0
  • t = (- 3± √3² -4*8*(-28))/16
  • t = (-3±√905)/16
  • t = 1.693 seconds (positive solution)

User Dramzy
by
6.3k points