• # question_answer Air (kinematic viscosity $=15\times {{10}^{-6}}{{\text{m}}^{\text{2}}}\text{/s}$) with a free stream velocity of 10 m/s flows over a smooth two- dimensional flat plate. If the critical Reynolds number is $5\times 10,$ what is the maximum distance from the leading edge up to which laminar boundary layer exists? A) 30 cm              B) 75 cmC) 150 cm             D) 300 cm

$v=15\times {{10}^{-6}}{{\text{m}}^{\text{2}}}\text{/s,}$ ${{U}^{\infty }}=10\,\text{m/s}$ ${{\operatorname{Re}}_{c}}=5\times {{10}^{5}}$  ${{\operatorname{Re}}_{c}}=\frac{{{U}_{\infty }}x}{v}$ $x=\frac{5\times {{10}^{5}}\times 15\times {{10}^{-6}}}{10}=0.75\,m\,\,or\,\,75\,cm$