A $100-g$ mass, $M,$ is placed at the end of a $50-mm$ steel beam with $5-mm$ cross$-$sectional diameter. This assembly is placed in a centrifuge to rotate the mass at speed, resulting in an elongation of the steel beam. The mass has a clearance of $1$ mm to the centrifuge wall. The rotational speed $($rev$/$s$)$ of the beam$/$mass assembly that would cause the mass to come into contact with the wall is most nearly: