SSC JE Mechanical Engineering 2018 Set 2 Paper

"The friction factor 'f ' at a given Reynold number in the turbulent depends on the relative roughness, defined as the ratio of average roughness to the diameter
$\mathrm{f}=\frac{64}{{\mathit{R}}_{\mathit{e}}}$ for Laminar flow
$\mathrm{f}=\frac{.316}{{\left({\mathit{R}}_{\mathit{e}}\right)}^{1∕4}}$ for turbulent flow