Answer:
d. 6 seconds
e. 12 seconds
Explanation:
Given that a projectile has an altitude of 320 feet at 2 seconds and 10 seconds after launch, you want to know the time to maximum height and the time the projectile lands on the ground.
d. Symmetry
The parabolic path is symmetrical about the vertical line through its vertex. So, the time at maximum height is the average of the two times at which the height is 320 ft:
(2 s + 10 s)/2 = (12/2) s = 6 s
The projectile is at maximum height 6 seconds after launch.
e. Landing
The projectile is launched from ground level at t=0, so will reach ground level again an equal time after reaching maximum height.
2 × (6 s) = 12 s
The projectile will land after 12 seconds.