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Question

Physics Question on Surface tension

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 =7.2×10−2N/m2=7.2\times {{10}^{-2}}N/{{m}^{2}} )

A

3.6×10−3N3.6\times {{10}^{-3}}N

B

3.4×10−10N3.4\times {{10}^{-10}}N

C

3.0×10−5N3.0\times {{10}^{-5}}N

D

3.8×10−11N3.8\times {{10}^{-11}}N

Answer

3.6×10−3N3.6\times {{10}^{-3}}N

Explanation

Solution

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