Question

A pendulum consists of a uniform disk with radius r = 10 cm and mass 545 g attached to a uniform rod with length L = 500 mm and mass 300 g. (figure: one end of the rod attach to a pivot and the other end attach to the center of the disk)

(a) Calculate the rotational inertia of the pendulum about the pivot.

(b) What is the distance between the pivot and the center of mass of the pendulum?

(c) Calculate the period of oscillation.

Plz help. Thanks.

Let me analyze your thinking. This is straightforward.

I thought I can find (a) by adding the rotational inertia of the rod and the disk.
I = 1/3 ML^2 + 1/2 mr^2
I wander in this case, what's the rotational inertia of the disk? Is that
I=1/2 mr^2?

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