# A train rounds an unbanked circular bend of radius 50 m at a speed of $54\;km\;h^{-1}$. If $g= 10 \;m/s^{-2}$, the angle of banking required to prevent wearing out of rails is given by
$\begin{array}{1 1} \theta= \tan^{-1}(0.15) \\ \theta=\tan^{-1}(0.25) \\ \theta= \tan^{-1} (0.35) \\ \theta= \tan^{-1}(0.45) \end{array}$