Answer:
The debris will be at a height of 56 ft when time is <u>0.5 s and 7 s.</u>
Step-by-step explanation:
Given:
Initial speed of debris is, 
The height 'h' of the debris above the ground is given as:

As per question,  . Therefore,
. Therefore,

Rewriting the above equation into a standard quadratic equation and solving for 't', we get:

Using quadratic formula to solve for 't', we get:

Therefore, the debris will reach a height of 56 ft twice. 
When time  during the upward journey, the debris is at height of 56 ft.
 during the upward journey, the debris is at height of 56 ft. 
Again after reaching maximum height, the debris falls back and at  , the height is 56 ft.
, the height is 56 ft.