Physics quiz question: stone-pound-ounces-kilogram unit conversions

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

The "stone" unit historically used in Scotland was the equivalent of 17 lbs 8 oz, or 7.936 kg. If there are 16 ounces (oz) in 1 pound (lb), then a kilogram (kg) is equivalent to:
(A) 2.83×10^–2 oz.
(B) 2.21 oz.
(C) 35.3 oz.
(D) 2.22×10³ oz.

[*] wki.pe/Stone_(unit).

Correct answer (highlight to unhide): (C)

Starting with the original conversion factor between kilograms and stone:

7.936 kg = 1 stone,

and stone to pounds and ounces, converting pounds to ounces:

7.936 kg = 17 lbs + 8 oz,

7.936 kg = 17lb·((16 oz)/(1 lb)) + 8 oz,

7.936 kg = 272 oz + 8 oz,

7.936 kg = 280 oz,

then with this equivalency between kilograms and ounces:

1 kg = (280 oz)/7.936 = 35.2822580645 oz,

or to three significant figures, a kilogram is 35.3 oz.

(Response (A) is (7.936/280); response (B) is (17.5/7.936); response (D) is (280×7.936).)

Sections 70854, 70855
Exam code: quiz01D4mP
(A) : 6 students
(B) : 6 students
(C) : 42 students
(D) : 3 students

Success level: 72%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.49