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JEE Mains · Physics · STD 11 - Fluid mechanics
  • JEE Mains 2020
  • Hard
  • MCQ

Consider a solid sphere of radius \(\mathrm{R}\) and mass density \(\rho(\mathrm{r})=\rho_{0}\left(1-\frac{\mathrm{r}^{2}}{\mathrm{R}^{2}}\right),  0<\mathrm{r} \leq \mathrm{R} .\) The minimum density of a liquid in which it will float is

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Answer & Solution

Correct Answer

(D) \(\frac{2\rho_{0}}{5}\)

Step-by-step Solution

Detailed explanation

In case of minimum density of liqued, sphere will be floating while completely submerged So \(\mathrm{mg}=\mathrm{B}\)

\(\mathrm{m}=\int_{0}^{\mathrm{R}} \rho\left(4 \pi \mathrm{r}^{2} \mathrm{dr}\right)=\mathrm{B}\)

\(=\rho_{0} \int_{0}^{R}\left(1-\frac{r^{2}}{R^{2}}\right) 4 \pi r^{2} d r=\frac{4}{3} \pi R^{3} \rho_{\ell} g\)

On Solving

\(\rho_{\ell}=\frac{2 \rho_{0}}{5}\)

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