Answer:
6.5 seconds.
Explanation:
Given: h=-16t²+679
When the object reaches the ground, h=0.
∴ 0=-16t²+679
collecting like terms,
⇒ 16t²=679
Dividing both side of the equation by the coefficient of t² i.e 16
⇒ 16t²/16 = 679/16
⇒ t² = 42.25
taking the square root of both side of the equation.
⇒ √t² =√42.25
⇒ t = 6.5 seconds.
