What about the component of Newton's Second Law in the radial direction?
Recall that the bob doesn't move in the radial direction since . By Newton's Second Law the tension T in
the rod, the radial component of the force due to gravity, and the
radial acceleration of the mass are in balance:
What is Fr?
It can be shown that the radial acceleration is given by
Now substitute these expressions for ar and Fr into the equation Fr=mar and solve for T.
What is the tension in the rod?