Q.

An open-ended U-tube of uniform cross-sectional area contains water (density 103 kg m-3). Initially the water level stands at 0.29 m from the bottom in each arm. Kerosene oil (a water-immiscible liquid) of density 800 kg m-3 is added to the left arm until its length is 0.1 m, as shown in the schematic figure below. The ratio (h1h2) of the heights of the liquid in the two arms is                           [2020] 

1 1514  
2 3533  
3 76  
4 54  

Ans.

(2)

Pressure will be same at the same horizontal level.

∴  PA=PB

⇒P0+ρkg×0.1+ρwg×(h1-0.1)=ρwgh2+p0

⇒80+1000(h1-0.1)=1000h2

⇒80+1000h1-100=1000h2

⇒h1-h2=201000

⇒h1-h2=0.02        ⋯(i)

Also, h1-0.1+h2=2×0.29

⇒h1+h2=0.68             ⋯(ii)

Solving (i) & (ii), we get

      2h1=0.70

   ⇒h1=0.35 m

and h2=0.33 m

So, h1h2=3533