## 20151121

### Physics quiz question: moment of inertia of LP record

Physics 205A Quiz 5, fall semester 2015
Cuesta College, San Luis Obispo, CA

"I have a vinyl fetich"
Christmas Junkie
flic.kr/p/fFwATx

An LP record[*] has a rotational inertia of 1.46×10–3 kg·m2, and rotates at a rate of 3.5 rad/s. The record can be considered a solid disk (Idisk = (1/2)·M·R2). If the LP record then rotates at a slower rate, it would have __________ rotational inertia.
(A) more.
(B) the same.
(C) less.
(D) (Not enough information is given.)

[*] Peter Atkins, Julio de Paula, Physical Chemistry (9th ed.), W.H. Freeman and Co. (2009), p. 318.

Correct answer (highlight to unhide): (B)

Since rotational inertia of the LP record depends on its mass M and radius R, which do not physically change whether rotating at a faster or slower rate, then the rotational inertia remains constant.

Sections 70854, 70855, 73320
Exam code: quiz05bL8D
(A) : 24 students
(B) : 32 students
(C) : 9 students
(D) : 0 students

Success level: 48%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.74