Two masses m and $\frac{\mathrm{m}}{2}$ are connected at the two ends of a massless rigid rod of length l. The rod is suspended by a thin wire of torsional constant k at the centre of mass of the rod-mass system (see figure). Because of torsional constant k, the restoring torque is $\mathrm{\tau }=\mathrm{k\theta }$ for angular displacement $\mathrm{\theta }$ . If the rod is rotated by ${\mathrm{\theta }}_0$ and released, the tension in it when it passes through its mean position will be: