TargetIIT

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difference in pressure on either side of fluid...

its 4 others to try or ur doubt? if u want xplanantion i can give it or else leave it 4 others

What I feel is

so pv=nRT neither T nor n changes so only thing that can happen is v increases..
This happens in two ways..

first if the cardboard is little flexible it slightly bulges in the center thus increasing volume
and also card comes a little below (looses contact with glass ) and remain sttuck due to surface tension with glass (water in between glass and card)

Both together adds to increase in volume.

You can try slide the card it slides smoothly(and water falls ofcourse ;) because of water in b/w

the pressure inside is due to the liquid and the gas which is less than the atmospheric pressure acting outside

actaully i missed the 3rd point..

a little of water escapes while tilting thus increasing volume for air..

@qwerty the weight of liq is same..

waht we are ending in is a long lost post abt  P + [b]h2 g[/b] = P1 and weight of water

i can't figure out ur eqns.. what are P1 and P and wht are hts..

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look i now have a separate viewpoint on this....


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in the glass we all know air pressure is same on either end...

now,

in the downward side, ie the cardboard, the upward force acting=P[ss]A[/ss]Xarea of cardboard..

on upward side, downward force=P[ss]A[/ss]Xarea of fluid..

thus net upward force=P[ss]A[/ss]X(area of cardboard-area of fluid surface)

now we can see that area of card board must be higher that the upper liquid surface for the cardboard to cover the tumbler completely..

and P[ss][ss]A[/ss][/ss] is a huge amount so the net upward force is HUGE.. which balances the downward weight!!

that is my viewpoint...awaiting replies!!