A spherical particle with $\mathrm{SG}=2.5$ and a diameter of $2 \mathrm{~mm}$ is immersed in water in a cylindrical centrifuge with a diameter of $20 \mathrm{~cm}$. If the particle is initially $8 \mathrm{~cm}$ above the bottom of the centrifuge and $1 \mathrm{~cm}$ from the centerline, what is the speed of the centrifuge (in rpm) if this particle strikes the wall of the centrifuge just before it hits the bottom?