U-tube: water 18 cm, liquid 0.9 g/cm³

The left arm of a U-tube holds water to a height of 18 cm, and the right arm holds another liquid of density 0.9 g/cm³ (water density 1.0 g/cm³). At rest, how high is the liquid column in the right arm, and what is the height difference between the two liquid surfaces?

Step-by-step

1. ρ_object = 1 , ρ_fluid = 1
   Comparing the object's density with the liquid's tells you whether it floats

Why it works

The same pressure acts at the bottom of both arms, so ρ_water × h_water = ρ_liquid × h_liquid. A less dense liquid stands higher than water, and the height difference is the gap between the two surfaces.

Common mistakes

• Assuming the two surfaces must be level because it is a U-tube.
• Getting the height difference as 18 cm plus 20 cm instead of their difference.

Related

u-tube-two-liquids-level-difference echo-well n-phy-buoyancy-float-1