Question

The length of a needle floating on water is 2.5 cm. Calculate the added force (due to surface tension) required to pull the needle out of water. (Surface tension of water $ =7.2\times {{10}^{-2}}N/{{m}^{2}} $ )

• A. $ 3.6\times {{10}^{-3}}N $
• B. $ 3.4\times {{10}^{-10}}N $
• C. $ 3.0\times {{10}^{-5}}N $
• D. $ 3.8\times {{10}^{-11}}N $

Answer 1

Answer: (A)

The force of surface tension $ F=T-2l $ $ =7.2\times {{10}^{-2}}\times 2\times 2.5\times {{10}^{-2}} $ $ =3.6\times {{10}^{-3}}N $