A 7500 kg National Geographic Submarine is submerging vertically down into deep ocean waters at constant speed. The buoyancy force pushing it upward is 75% of its weight. It takes 2.5 minutes for the submarine to reach a depth of 150 m starting from the surface without using its engine. 1. What is the mechanical energy of the submarine at the surface? 2. What is the mechanical energy of the submarine at the 150 m depth? 3. Is the mechanical energy of the Submarine conserved, increased, or decreased? Explain your choice. 4. What is the work done by each force acting on the Submarine