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1. The initial PE is mgh.

The final PE should be (mgh)/2

Initial - final = (mgh)/2

However, this is the wrong answer.
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2. Remember that the centre of mass of the water (for the purpose of calculating PE=mgh) is at a height ½h at the start. (Not h) When the container is half full, the centre of mass of the water is at a height ¼h

On the right, the water rises to fill half the container.
Its centre of mass will be at a height ¼h.
3. (Original post by Stonebridge)
Remember that the centre of mass of the water (for the purpose of calculating PE=mgh) is at a height ½h at the start. (Not h) When the container is half full, the centre of mass of the water is at a height ¼h

On the right, the water rises to fill half the container.
Its centre of mass will be at a height ¼h.
Ah, yes, yes. How stupid of me....

Could you look at this query of mine too ?

http://www.thestudentroom.co.uk/show....php?t=1585586
4. (Original post by Ari Ben Canaan)
Ah, yes, yes. How stupid of me....

Could you look at this query of mine too ?

http://www.thestudentroom.co.uk/show....php?t=1585586
Sure, no problem. Done.

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