A non-conducting non-magnetic rod having circular cross section of radius R is  suspended from a rigid support as shown in figure. A light and small coil of 3000 turns is  wrapped tightly at the left end of the rod where uniform magnetic field B exists in  vertically downward direction. Air of density $\rho$ hits the half of the right part of the rod  with velocity V as shown in the figure. What should be current in clockwise direction (as  seen from O) in the coil so that rod remains horizontal? Give answer in mA. 
Given : $\frac{2}{LV}\sqrt{\frac{\pi RB}{\rho }}=\frac{1}{\sqrt{5}}{A}^{-1/2}$ [Assume air stops after collision]