Question

I am confused.
The answer is B...
But what is the basic concept/formula that I need to solve similar questions?
In attached file.

Answer 1

Compare the initial situation to the final situation. Ask yourself what was the mass of water that was actually moved and how far was it moved vertically.

Answer 2

remember the potential energy lost in a uniform gravitational field is gMH where g is acceleration due to gravity M is the mass moved and H is the distance moved.

Answer 3

Half the mass (m/2) moves to a position h/2 lower.......

Answer 4

yeah that makes a lot of sense but
how is it by 4?
mgh/4...

Answer 5

And why..

Answer 6

Thanks :)

Answer 7

@aaronq
@Mashy