Aj universal diving photography

Originally suspended at a deeper depth, buoyancy equals gravity.

If you want to rise, you should drain some water. You mean to discharge 50N water. At this time, gravity is less than buoyancy, and the resultant force on the submarine is upward, so the submarine rises.

When it rises to the ideal depth, it is to add water to the submarine, so that gravity becomes larger, until it equals buoyancy again, and the submarine can change from rising to suspension.

During the whole process, if the submarine does not surface, its buoyancy will remain unchanged. Formula F float = ρ water gV row, so it can be seen that ρ water and V row remain unchanged, and F float remains unchanged.