Question

A wire of length I metres, made of a material of specific gravity 8 is floating horizontally on the surface of water. If it is not wet by water, the maximum diameter of the wire (in millimetres) up to which it can continue to float is : (surface tension of water is $T=70\times {10}^{-3}N{m}^{-1}$ )

• A. 1.5
• B. 1.1
• C. 0.75
• D. 0.55

Answer 1

Answer: (B)

$T.l=v\rho g$ or $T.l=\pi r^{2}l\rho g$ or $T=\pi r^2\rho g$ $\therefore$ $70\times {10}^{-3}=3.14\times r^2\times 8\times {10}^{-3}\times 9.8$ or $r^2=\frac{70\times {10}^{-3}}{3.14\times 8\times {10}^{-3}\times 9.8}=0.28$ $\therefore$ Minimum diameter of the wire =2r $=2\times 0.53$ $\approx 1.1m$