# NEET Physics Mechanical Properties of Fluids Questions Solved

Radius of a soap bubble is 'r', surface tension of soap solution is T. Then without increasing the temperature, how much energy will be needed to double its radius

(a) $4{\mathrm{\pi r}}^{2}\mathrm{T}$                        (b) $2{\mathrm{\pi r}}^{2}\mathrm{T}$

(c) $12{\mathrm{\pi r}}^{2}\mathrm{T}$                       (d) $24{\mathrm{\pi r}}^{2}\mathrm{T}$

(d) $\mathrm{W}=8\mathrm{\pi T}\left({\mathrm{R}}_{2}^{2}-{\mathrm{R}}_{1}^{2}\right)=8\mathrm{\pi }\left[\left(2\mathrm{r}{\right)}^{2}-\left(\mathrm{r}{\right)}^{2}\right]=24{\mathrm{\pi r}}^{2}\mathrm{T}$

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