What would be the most energy efficient way to sink a floating object of 1 square kilometre in area 300 feet below the surface of water (or in other words drag it to the bottom). The method should not include putting a weight above the surface of floor or attaching a weight to the object. Hydraulics? Some sort of simple machine such as lever etc. How much energy in kilowatts/hour is roughly needed to sink this object? A few megawatts, hundreds of megawatts or thousands of megawatts? Remember the object is barely floating and applying just barely a small force makes it start to go underwater. The object is 1 square km in area. It has a mass which is just enough buoyant to keep it floating.

So what is your opinion. Note we don't do homework or science projects for you.

Simply dropping a weight on it would be more efficient than building any elaborate mechanism. Applying a force would have to be sustained so that it doesn't float back up. But hey, do the math--maybe you could work for the government some day.

Putting a hole in it is pretty efficient.

Regarding power, the formula for it is force times velociity. Given that the object is barely buoyant it would take only a small force to sink it, and if you don't care how long it takes to sink then velocity may be small as well. Hence the power required may be quite small.