A torsion pendulum consists of a metal disk with a wire running through its center and soldered in place. The wire is mounted vertically on clamps and pulled taut. Figure a gives the magnitude ? of the torque needed to rotate the disk about its center (and thus twist the wire) versus the rotation angle ?. The vertical axis scale is set by ?s = 4.0 x 10-3 N ? m. The disk is rotated to ? = 0.200 rad and then released. Figure b shows the resulting oscillation in terms of angular position ? versus time t. The horizontal axis scale is set by rs = 0.40 s.(a) What is the rotational inertia of the disk about its center?(b) What is the maximum angular speed d?/dt of the disk? (Caution: Do not confuse the (constant) angular frequency of the SHM with the (varying) angular speed of the rotating disk, even though they usually have the same symbol w.

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0.10 0.20 e (rad) (a) 0.2 (s) -0.2 (per) e r(10N• m)