20110905

Physics quiz question: "hellasecond"

Physics 205A Quiz 1, fall semester 2011
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problems 1.30, 22.15, 22.20

Given that the speed of light in vacuum is 3.00e+8 m/s, how many meters would light travel in 1 Hs (1 "hellasecond" = 10^27 s)?
(A) 3.33e–36 m.
(B) 3.00e–19 m.
(C) 3.33e+18 m.
(D) 3.00e+35 m.

Correct answer: (D)

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

c (m/s) = ∆x (m)/∆t (s),

such that solving for ∆x gives:

∆x = c*∆t = (3.00e+8 m/s)*(1e+27 s) = 3.00e+35 m.

Response (A) is 1/(c*∆t); response (B) is v/∆t, and response (C) is ∆t/c.

Sections 70854, 70855
Exam code: quiz01unI7
(A) : 3 students
(B) : 10 students
(C) : 1 student
(D) : 42 students

Success level: 74%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.33

Compare to results of a similar "hella-" problem asked of second-semester college physics students (fall semester 2010).

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