Given, the wheel's radius $=\mathrm{2 }\text{m},$

velocity $=\mathrm{4 }{\text{m s}}^{-1}$

As velocity is uniform, therefore acceleration experienced by the wheel in a circular motion,

$a=\frac{v^2}{r}=\frac{{\left(4\right)}^2}{2}=8 \mathrm{m} {\mathrm{s}}^{-2}$

$\therefore$ Relative acceleration of the topmost point of the wheel with respect to the bottom-most point of the wheel

${=\; a}_T{-\; a}_B$

$=8-\left(-8\right)=16 {\text{m s}}^{-2}$