Answer:
After 3 seconds while going up and 6 seconds while coming down
Step-by-step explanation:
Since projectile is launched from ground level with an initial velocity of v 0 feet per second, initial height =0
Height is given by
where v0 = initial velocity = 144
a) When h =288 ft.
At t= 3 or 6 seconds the projectile would be at height 288 ft.
So while going up after 3 seconds it wouldbe at a height of 288 ft and while coming after 6 seconds.