Question

A ring having radius $2.5\text{cm}$ and mass $10\text{gram}$ floats on a liquid surface having surface tension $0.06\text{N/m}$. Find force required to just lift the ring from liquid surface.

• A. $0.06\text{N}$
• B. $0.12\text{N}$
• C. $0.24\text{N}$
• D. $0.03\text{N}$

Answer 1

The correct option is B $0.12\text{N}$

As inner and outer surface of ring are in contact with water surface
$F=4\pi rT+Mg$
$=4\times 3.14\times (2.5\times {10}^{-2})\times 0.06+(10\times {10}^{-3})\times 9.8$
$=0.01884+0.098=0.12\text{N}$