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JEE Mains · Physics · STD 11 - Fluid mechanics
  • JEE Mains 2015
  • Hard
  • MCQ

If it takes \(5\,minutes\) to fill a \(15\,litre\) bucket from a water tap of diameter \(\frac{2}{{\sqrt \pi  }}cm\) then the Reynolds number for the flow is (density of water \(= 10^3\,kg/m^3\) ) and viscosity of water \(= 10^{-3}\,Pa.s\) ) close to

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Answer & Solution

Correct Answer

(D) \(5500\)

Step-by-step Solution

Detailed explanation

Given: Diameter of water tap \( = \frac{2}{{\sqrt \pi  }}\,cm\)

\(\therefore \,\,Radius,\,r = \frac{1}{{\sqrt \pi  }} \times {10^{ - 2}}\,m\)

\(\frac{{dm}}{{dt}} = \rho AV\)

\(\frac{{15}}{{5 \times 60}} = {10^3} \times \pi {\left( {\frac{1}{{\sqrt \pi  }}} \right)^2} \times {10^{ - 4}}V\)

\( \Rightarrow V = 0.05\,m/s\)

Reynold's number, \({R_e} = \frac{{\rho Vr}}{n}\)

\( = \frac{{{{10}^3} \times 0.5 \times \frac{2}{{\sqrt \pi  }}{{10}^{ - 2}}}}{{{{10}^{ - 3}}}} \cong 5500\)

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