A tank 36 ft. by 36 ft. by 6 ft. is filled with water to a depth of 5 ft. If a bulkhead is placed in the center of the tank running fore-and-aft along the 36-foot axis, how will the value of the moment of inertia of the free surface be affected?

Correct Answer: Option C — The moment of inertia would be 1/4 its original value.

The moment of inertia of a free surface is proportional to the cube of the breadth (I = lb³/12). By installing a longitudinal bulkhead, the breadth of each compartment is halved. Since (1/2)³ equals 1/8, and there are two such compartments, the total moment of inertia is reduced to 1/4.