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JEE Mains · Physics · STD 11 - Fluid mechanics
  • JEE Mains 2026
  • Hard
  • Numerical

Sixty four rain drops of radius 1 mm each falling down with a terminal velocity of \(10 cm / s\) coalesce to form a bigger drop. The terminal velocity of bigger drop is _________ \(cm / s\).

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Answer & Solution

Correct Answer

(C) 160

Step-by-step Solution

Detailed explanation

\(V _{ T }=\frac{2 r ^2 g}{9 n }[\sigma-\rho]\)
\(V _{ T } \propto r ^2\)
image
64 drop
\(64\left(\frac{4}{3} \pi R_1^3\right)=\frac{4}{3} \pi R_2^3\)
\(R _2=4 R _1\)
\(\frac{\left( V _{ T }\right)_1}{\left(V_{ T }\right)_2}=\left(\frac{ R _1}{ R _2}\right)^2=\left(\frac{1}{4}\right)^2\)
\(\frac{10}{\left(V_{ T }\right)_2}=\frac{1}{16}\)
\(\left( V _{ T }\right)_2=160 cm / sec\)
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