
Apply W.E.T. from A to B $\begin{aligned}
& \Rightarrow \mathrm{W}{\mathrm{mg}}=\mathrm{K}{\mathrm{B}}-\mathrm{K}{\mathrm{A}} \
& \Rightarrow \mathrm{mg} \times\left(\frac{\mathrm{R}}{\sqrt{2}}+\mathrm{R}\right)=\frac{1}{2} \mathrm{mv}{\mathrm{B}}^2-0\left{\mathrm{v}{\mathrm{A}}=0 \text { rest }\right} \
& \Rightarrow \mathrm{mgR} \frac{(\sqrt{2}+1)}{\sqrt{2}}=\frac{1}{2} \mathrm{mv}{\mathrm{B}}^2 \
& \Rightarrow \sqrt{\mathrm{gR} \frac{2(\sqrt{2}+1)}{\sqrt{2}}}=\mathrm{v}{\mathrm{B}} \
& \Rightarrow \sqrt{\frac{10 \times 14 \times 2(2.4)}{1.4}}=\mathrm{v}{\mathrm{B}} \
& \Rightarrow 21.9=\mathrm{v}_{\mathrm{B}}
\end{aligned}$
