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
  • A
    $1100$
  • B
    $11,000$
  • C
    $550$
  • $5500$

Answer

Correct option: D.
$5500$
d
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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