Answer:
after 21 seconds
Step-by-step explanation:
Given
h = - 16t² + 272t + 1344
When the ball strikes the ground then h = 0, that is
- 16t² + 272t + 1344 = 0 ( divide through by - 16 )
t² - 17t - 84 = 0 ← in standard form
(t - 21)(t + 4) = 0 ← in factored form
Equate each factor to zero and solve for t
t - 21 = 0 ⇒ t = 21
t + 4 = 0 ⇒ t = - 4
However t > 0 thus t = 21
The ball strikes the ground after 21 seconds.
