IIT JEE , AIEEE Forum - Physics , Mechanics

rohith291991

plz help me...the question is to find the velocity of the water at point B .....in the solution they say that pressure at P =pressure at B....velocity at P is same as velocity at B but there is a potential energy difference between P and B!!!!!! where does the energy go!!! and another doubt is....if water is considered incompressible....then in a steady streamline....is it that the magnitude of velocity at all points must be same ????? if so how come when u apply bernoullis theorem to water flowing in a tube....and if p1+rowgh1 is not equal to p2+rowgh2....then we get that v1 not equal to v2....but the liquid is incompressible and this is not the case!!!! what is the flaw!!!!??????

ayshwarya

oyy wers B here?

rohith291991

its given right....at the bottom of the siphon...anyway sorry for the bad diagram...

ayshwarya

ok sorry my frnd i found it out

ananth_patri

i think we can apply Bernoiulli equn only 4 incompresseble liquids...so if the ques is about compressible liq...then it involves higher mathematics.......__

rohith291991

no question is about incompressible liquids only....

ayshwarya

see yaar 2 do a work v need energy n any machine on earth is not 100% efficient 2 raise d water upwards v require some energy if u wait 4 few more minutes i wud try 2 calculate d energy

ananth_patri

if its about incompressable liiq, then apply bernoulli equ at A and at B and get the vel by applying the equ of continuty ..???

ayshwarya

aree yaar see here in a stream line flow d velocity of a iven particle is not same at all points its actually : if v consider a point P den d velocity of a given liquid at P is constant
n 1 more my frnd see by bernoulli principle

P1 +pgh1 +1/m1v1^2 = P2 +pgh1 + 1/2 m2v^2

ananth_patri

thts right as ayshwarya posted we've got toapply Bernoulii theroem...and equ of continuty

rohith291991

yes u are right thanks....but then i must say that the solution given is wrong right???? i mean...they say that vp=vb but this is not possible.....ok thanks.... that means that incompressible liquid doesnt mean speed at ALL points is constant....but in the solution they are taking like that...

LAMPARD

Actually,they maybe right to some extent...
see,P and A are at the same horizontal level and we know that pressure at pts. at same horizontal level is same
since pressure at A is atm. pressure,pressure at P is also atm. pressure
pressure at B is also atm. pressure as seen in the diag...thus pressure at P=pressure at B..

rohith291991

well mainly im not concerned about the pressure...im concerned about the "same velocity" thing.....

LAMPARD

Are A and P along the same line???

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