Two masses $m$ and $\frac{m}{2}$ are connected at the two ends of a massless rigid rod of length $I$. 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 $\tau=\mathrm{k} \theta$ for angular displacement $\theta$. If the rod is rotated by $\theta_0$ and released, the tension in it when it passes through its mean position will be: