## 20170917

### Physics quiz question: critical damping coefficient units

Physics 205A Quiz 1, fall semester 2017
Cuesta College, San Luis Obispo, CA

The damping ratio ζ is a dimensionless physical constant[*] used to describe the damping of masses on springs:

ζ = cc/√(km).

The spring constant k is measured in units of kg·s–2, and the mass m is measured in units of kg. The units for the critical damping coefficient cc are:
(A) s.
(B) kg·s–1.
(C) kg–1·s.
(D) s–1.

[*] wki.pe/Damping_ratio.

Correct answer (highlight to unhide): (B)

Starting with the expression for the critical damping coefficient cc:

cc￼ = ζ·√(km),

and replacing the quantities in the equation with their kg and s units (and ζ is a dimensionless physical constant with no units), the units of cc￼ are:

cc￼￼ = √(kg·s–2·kg),

cc￼ = √(kg2·s–2),

cc￼ = kg·s–1.

Sections 70854, 70855
Exam code: quiz01D4mP
(A) : 0 students
(B) : 42 students
(C) : 13 students
(D) : 2 students

Success level: 72%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.33