Question

Why are ballast tanks important in submarines?
A. Enhance the look of the submarine.
B. Help to maintain the pressure of the submarine.
C. Help to decrease the weight of the submarine.
D. Help in the floatation of the submarine by storing and removing water in them when required.

Answer 1

Hint: A submarine usually consists of two ballast tanks that are located at the front and rear. When the tank is filled with water its density increases and the submarine can go deep in water and when the tank is empty its density decreases and it can float.

Complete step by step answer:
The fundamentals of floatation and Archimedes principle are used to arrive at the equation of floatation of a submarine, i.e., in either submerged or surfaced condition, the weight of the submarine is equal to the buoyancy force acting on it.
For a surfaced submarine to submerge, the weight of the submarine has to increase. It is only then that in submerged condition, the buoyancy on the volume of the submarine above the waterline can be balanced by the additional weight.
In submarines ballast tanks are used to balance the buoyancy of the vessel. There are two very large tanks outside of the pressure hull on either end of the submarine. When the ballast tanks will be filled with water the buoyancy will be reduced and hence the submarine will sink and whereas when they are emptied it will be less dense than water and hence the submarine will float.
Therefore, the ballast tanks are important for floatation by storing and removing water in them when it's required.

Hence, the correct option is D.

Note:
This should be noted that Archimedes principle is applied to submarines just as it did for surface ships, the only difference is that the submerged volume is equal to the entire hull volume.