Two masses m and $m\over2$ 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 $\tau=k\theta$ for angular displacement 0. If the rod is rotated by θ_{0} and released, the tension in it when it passes through its mean position will be:

(1) $3k\theta_0^2\over l$

(2) $k\theta_0^2\over2l$

(3) $2k\theta_0^2\over l$

(4) $k\theta_0^2\over l$