$10.$It is required to obtain a highly turbulent stream for a water stream by reducing the diameter of the pipe. Initially, water flows in a $4-$in ID pipe with a flow rate of $50\frac{g}{sec}$ at $60C.$ To what extent diameter should be reduced?

$($a$)$ If just turbulence is required $($b$)$ If Reynolds number is to be kept at $10000.$