Two identical balls A and B of equal mass are lying on a smooth surface as shown in the figure. If ball 'A' hits ball 'B' at rest with a velocity $16 \mathrm{~ms}^{-1}$, then the co-efficient of restitution between $A$ and $B$ so that $B$ just reaches the highest point of the smooth inclined plane is $\left(\mathrm{g}=10 \mathrm{~ms}^{-2}\right)$