Need to find torque so I can find the period

[auk411]

Homework Statement

A long uniform rod of mass .6 kg is free to rotate in horizontal plane about a vertical axis through its center. A spring with force constant k = 1850 N/m is connected horizontally between one end of the rod and a fixed wall. When the rod is in equilibrium, it is parallel to wall. What is the period of the small oscillations that result when the rod is rotated slightly an released?

Homework Equations

Torque = - C (a constant) \theta

T (period) = 2\pi\sqrt{I/C}.

The Attempt at a Solution

So, I can find I (the moment of inertia), but what I can't find is what the constant is supposed to be. I've been told to find the torque as a function of \theta. I just don't know how.

Also, I do realize that it's important that we are working with small angles.

It probably doesn't help that I can't really picture what is going on either.

 

[ehild]

You need the spring force to get the torque. It depends on the change of length of the spring. Calculate the length change of the spring if the rod rotates by a small angle θ.


ehild