Calculating the Frequency of Oscillation for an Oscillating Gate with Spring

[AdMitch]

I need to find the frequency with which the gate will swing in Rad/s. I know the mass is 2kg, the moment of inertia about the hinges is 0.36kgm² and that the torsional spring stiffness is 18.2Nm/rad. A person pushes the gate open to 90degrees and then it's released. Damping is negligible. If you could just point me in the right direction i'd like to give it a go on my own but i just don't know where to start.

 

[trambolin]

it is very similar to $F=ma$ for normal springs and masses

$I\ddot\theta = ??$

Can you complete the equation? (I is inertia)