Question

A flat disk, a solid sphere, and a hollow sphere each have the same mass m and radius r. The three objects are arranged so that an axis of rotation passes through the center of each object. The rotation axis is perpendicular to the plane of the flat disk. Which of the three objects has the largest rotational inertia?
a) The solid sphere and hollow sphere have the same rotational inertia and it is the largest.b) The hollow sphere has the largest rotational inertia.c) The solid sphere has the largest rotational inertia.d) The flat disk has the largest rotational inertia.e) The flat disk and hollow sphere have the same rotational inertia and it is the largest.

Answer 1

Answer:

b)

Explanation:

Rotational inertia of the sphere: $\frac{2}{5}mr^2$

Rotational inertia of hollow sphere: $\frac{2}{3}mr^2$

Rotational inertia of flat disk: $\frac{1}{2}mr^2$

The largest value is 2/3 mr², therefore, hollow sphere's inertia is largest.