At the top most point of the bridge, wheels of the car will not lose contact with the bridge if 

$\begin{array}{l}\mathrm{V}\le \sqrt{\mathrm{Rg}}\\ \therefore {\mathrm{V}}_{\max }=\sqrt{\mathrm{gR}}\\ \Rightarrow 10=\sqrt{10\mathrm{R}}\Rightarrow \mathrm{R}=10\mathrm{m}.\end{array}$