A compound pendulum consists of a thin rod of length 1.4 m and a disc of radius 0.2 m. The centre of the disc is attached to the end of the rod and the pendulum pivots about the opposite end of the rod. Both the mass of the rod and the mass of the disc are the same, each being 3.9 kg. What is the period of the pendulum?
[g=9.81 ms/2, MI rod about its end 1/3mL[SUP]2[/SUP], MI disc through centre, perpendicular to the plane 1/2mr2]
Compound pendulum: T = 2π√(I/mgL)
The Attempt at a Solution
I tried adding the two inertias together for I = 1/3mL2 + 1/2mr2] but that didn't really work out. Since r<<L, I considered this to be a simple pendulum and used 1/2mr2] to find I in the compound pendulum equation, but this method was also incorrect. Am I supposed to use the parallel axis theorem? Should I have used the simple pendulum equation instead? Please help.