Surface tension

Question

A cube with a mass *m* = 20 *g* wettable by water floats on the surface of water. Each side of the cube has length *l* = 3 cm. The angle of contact between water and glass is zero degree and the surface tension of the water is 7.5 × ${10}^{-2}$ N/m. The distance between the lower face of the cube and the surface of the water is

Moderate

Solution

${\mathrm{F}}_{\mathrm{Uptthrust}}={\mathrm{F}}_{\mathrm{Surface}\mathrm{tension}}+\mathrm{Weight}$

${\mathrm{l}}^{2}\mathrm{xrg}=4\mathrm{lT}+\mathrm{mg}\phantom{\rule{0ex}{0ex}}{(.03)}^{2}\times {10}^{3}\times 10=.009+.2\phantom{\rule{0ex}{0ex}}9\mathrm{x}=.209\phantom{\rule{0ex}{0ex}}\mathrm{x}=.02322\mathrm{m}=2.322\mathrm{cm}$

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