9514 1404 393
Answer:
t = 1 1/7 ≈ 1.1429 seconds
Explanation:
Filling in the given height, we can solve for t:
640 = -490t^2 +1120t
49t^2 -112t +64 = 0 . . . . . divide by 10, put in standard form
(7t -8)^2 = 0
t = 8/7 . . . . . . . the value of t that makes the factor(s) zero
The model rocket will reach its maximum height of 640 cm after 1 1/7 seconds.