Physics quiz question: daily Red Bull® caffeine consumption rate

Physics 205A Quiz 1, fall semester 2015
Cuesta College, San Luis Obispo, CA

A single can of Red Bull® beverage containing 80 mg of caffeine[*] is consumed once a day. Assuming that no other caffeinated beverages are consumed, the average daily intake of caffeine in grams per second is:
(A) 1.2×10^–8 g/s.
(B) 2.8×10^–7 g/s.
(C) 9.3×10^–7 g/s.
(D) 2.2×10^–5 g/s.

[*] energydrink-us.redbull.com/caffeine-red-bull.

Correct answer (highlight to unhide): (C)

The intake in grams per second can be determined from converting the units from the given rate of 80 mg per day by setting up conversion factors such that unwanted units cancel (mg, day) while desired units remain (g, s):

(80 mg/day)·(1 g/1000 mg)·(1 day/24 h)·(1 h/60 min)·(1 min/ 60 s),

= 9.259259×10^–7 g/s,

which to two significant figures, is 9.3×10^–7 g/s.

(Response (A) is the result of ingesting 1 mg of caffeine a day; response (C) is the result of ingesting 1 mg of caffeine an hour, while response (D) is the result of drinking one Red Bull® beverage every hour; response (D) is the result of ingesting 1 g of caffeine every hour.)

Sections 70854, 70855, 73320
Exam code: quiz01rdBL
(A) : 4 students
(B) : 3 students
(C) : 72 students
(D) : 1 student

Success level: 90%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.21