Physics 205A Quiz 6, fall semester 2018
Cuesta College, San Luis Obispo, CA
the longest pendulum currently in existence is at the Oregon Convention Center in Portland, OR, a 40 kg mass swinging on a cable with a period of 9.25 seconds.[*] At that location the magnitude of the acceleration due to gravity g is 9.82611 m/s2.[**] The length of the cable for this pendulum is:
(A) 4.53 m.
(B) 14.5 m.
(C) 21.3 m.
(D) 209 m.
[*] Martin Beech, The Pendulum Paradigm: Variations on a Theme and the Measure of Heaven and Earth, BrownWalker Press (2014), p. 42.
[**] wolframalpha.com/input/?i=gravitational+acceleration+portland,+or.
Correct answer (highlight to unhide): (C)
The period of a pendulum is given by:
T = 2·π·√(L/g),
which does not depend on the mass. Since the period T = 9.25 s and gravitational constant g = 9.82611 m/s2 are known, the length L can then be solved for:
L = g·(T/(2·π))2,
L = (9.82611 m/s2)·((9.25 s)/(2·π))2 = 21.2963585648... m,
or to three significant figures, the length of the pendulum cable is 21.3 m.
(Response (A) is g·((2·π)/T)2; response (B) is g·T/(2·π); response (C) is ((g·T)/(2·π))2.)
Sections 70854, 70855
Exam code: quiz06POr7
(A) : 1 student
(B) : 3 students
(C) : 46 students
(D) : 2 students
Success level: 88%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.42
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