Physics quiz question: "hellameter"

Physics 205B Quiz 1, Fall Semester 2010
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 22.17

How long does it take light to travel 1 Hm (1 "hellameter" = 10^27 m) in vacuum?
(A) 3.33e–36 s.
(B) 3.00e–19 s.
(C) 3.33e+18 s.
(D) 3.00e+35 s.

Correct answer: (C)

The speed of light in vacuum is c = 3.00e+8 m/s, and the relation between speed, distance, and elapsed time is:

c = ∆x/∆t,

such that solving for time gives:

∆t = (∆x)/c = (3.00e+8 m/s)/(1e+27 m) = 3.33e+18 s.

Response (A) is 1/(c*∆x); response (B) is c/∆x, and response (D) is c*∆x.

Student responses
Section 70856
(A) : 0 students
(B) : 3 students
(C) : 7 students
(D) : 3 students

Success level: 54%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.75