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Question: Answered & Verified by Expert
A spherical body of density $\rho$ is floating half immersed in a liquid of density $d$. If $\sigma$ is the surface tension of the liquid, then the diameter of the body is
PhysicsMechanical Properties of FluidsAP EAMCETAP EAMCET 2018 (22 Apr Shift 2)
Options:
  • A $\sqrt{\frac{3 \sigma}{g(2 \rho-d)}}$
  • B $\sqrt{\frac{6 \sigma}{g(2 \rho-d)}}$
  • C $\sqrt{\frac{4 \sigma}{g(2 \rho-d)}}$
  • D $\sqrt{\frac{12 \sigma}{g(2 \rho-d)}}$
Solution:
1715 Upvotes Verified Answer
The correct answer is: $\sqrt{\frac{3 \sigma}{g(2 \rho-d)}}$


Weight of body
$=$ Buoyant force + Force of surface tension
$$
\begin{aligned}
\frac{4}{3} \pi r^3 \rho \times g & =\frac{2}{3} \pi r^3 d g+2 \pi r \sigma \\
\frac{2}{3} \pi r^3 g(2 \rho-d) & =2 \pi r \sigma
\end{aligned}
$$
So, $r^2=\frac{3 \sigma}{g(2 \rho-d)}$
So,
$$
r=\sqrt{\frac{3 \sigma}{g(2 \rho-d)}}
$$

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