Rolling without slipping

We know that the moment of inertia of the soccer ball is $I=\frac{2}{3}mr^2$ .

Hence, by the conservation of energy, we have $mgh=\frac{1}{2}mv^2+\frac{1}{2}I\omega^2\\=\frac{1}{2}mv^2+\frac{1}{2}\times\frac{2}{3}mr^2\times\frac{v^2}{r^2}\\=\frac{5}{6}mv^2$ Hence, $v=\sqrt{6g}=7.67$ .