The question asked was "what should be the acceleration such that the pressure at both the points marked by thick dots be equal? the vessel is open and cubic with side 5m?"
Initially i considered the diagram to be resembling the figure B where $$\tan(\theta)=a/g$$
but then i realized since the both points are the midpoints of the respective sides, the height of the liquid above the lower point must be half of the height above the point on the side. I took the diagram then to resemble D. Then i got the answer as $a=2g$. Is this CORRECT?
If this had been a closed vessel what would the answer have been? Figure C That is my question.