\(t =\frac{\text { Arc length }}{ v }=\frac{2 \pi \frac{ R }{4}}{ v }=\frac{\pi R }{2 v }\) average velocity,
\(\langle v \rangle =\frac{ AB }{ t }=\frac{ R \sqrt{2}(2 v )}{\pi R }=\frac{2 \sqrt{2} V }{\pi}\)
\(\Rightarrow \frac{ V }{\langle V \rangle} =\frac{\pi}{2 \sqrt{2}} .\)