Consider the situation in Example 12.6.

(a) Is the vector sum of the forces exerted by the shaft on the disc nonzero while the disc is spinning up?

(b) Is the disc isolated?

Data from Example 12.6

Consider the spinning disc shown in Figure 12.34, in which, a spinning conical shaft rises up into the opening in the center of the disc, and the disc begins to spin. Suppose the disc's rotational inertia is \(I_{\mathrm{d}}\), that of the shaft is \(I_{\mathrm{s}}\), and the shaft's initial rotational speed is \(\omega_{\mathrm{i}}\). Does the rotational kinetic energy of the disc-shaft system remain constant in this process? Assume for simplicity that no external forces cause torques on the shaft.

Figure 12.34 Example 12.6.