Cuesta College, San Luis Obispo, CA

A ring and a solid disk rotate about their centers. The ring and the solid disk each have the same mass of 1.2 kg. The ring has a radius of 0.25 m, and the solid disk has a smaller radius than the ring. (

*I*=

_{ring}*M*·

*R*

^{2},

*I*= (1/2)·

_{disk}*M*·

*R*

^{2}.)

The rotational inertia of the ring is __________ the rotational inertia of the solid disk.

(A) less than.

(B) equal to.

(C) greater than.

(D) (Not enough information is given.)

Correct answer (highlight to unhide): (C)

The rotational inertia of the ring of mass

*M*= 1.2 kg and radius

*R*= 0.25 m is:

*I*=

_{ring}*M*·

*R*

^{2}= (1.2 kg)·(0.25 m)

^{2}= 0.075 kg·m

^{2}.

The rotational inertia of the disk of mass

*M*= 1.2 kg and a radius

*smaller*than 0.25 m, along with the factor of (1/2) then must be

*smaller*than the rotational inertia of the ring:

*I*= (1/2)·

_{disk}*M*·

*R*

^{2}= (1/2)·(1.2 kg)·(some value less than 0.25 m)

^{2},

such that

*I*>

_{ring}*I*.

_{disk}Sections 70854, 70855

Exam code: quiz05nWaW

(A) : 6 students

(B) : 4 students

(C) : 39 students

(D) : 0 students

Success level: 80%

Discrimination index (Aubrecht & Aubrecht, 1983): 0.34