|B'S|=\frac{|VV'|\cdot\sqrt3}{2}\\|VV'|=2\cdot\frac{5}{\sqrt3}\cdot\frac{\sqrt3}{\sqrt3}=\frac{2\cdot5\cdot\sqrt3}{3}\\|VS|=\frac12|VV'|=h=\frac12\cdot \frac{2\cdot5\sqrt3}{3}=\boxed{\frac{5\sqrt3}{3}\ cm}