Given:
Time of travelling is, 14 hours.
Travelled height is 140 feet.
The objective is to find the height of the submarine after 5 hours.
Since, it is given that the submarine is descending at a constant rate.
Then, the constant speed can be calculated as,
Now, the height after 5 hours can be calculated as,
Hence, the height of the submarine in downwards after 5 hours is 50 ft.