Physics quiz question: Mountain Dew AMP(TM) caffeine consumption rate

Physics 8A Quiz 1, Fall Semester 2005
Cuesta College, San Luis Obispo, CA

Physics 8A learning goal Q1.1

(Cf. Young and Freeman, University Physics, 11/e, Exercise 1.6.)

[3.0 points.] Suppose that you drank a Mountain Dew AMP(TM) beverage (containing 113 mg of caffeine) twice a day. Which one of the following choices best describes your average intake of caffeine in grams per second, if you do not drink any other caffeinated beverage?
(A) 2.62 x 10^-6 g/s.
(B) 5.12 x 10^-5 g/s.
(C) 1.95 x 10^-4 g/s.
(D) 0.382 g/s.

Correct answer: (A)

The intake in grams per second can be determined from converting the units from the given rate of 226 mg per day:

(226 g/1 day) * (1 g/1,000 mg) * (1 day/24 h) * (1 h/3600 s).

Response (B) is the result of 1,000/(226*3600*24); response (C) is 226*3,600*24/1000, but with the resulting 10^4 exponent switched to 10^-4; while response (D) is 3,600*24/(226*1,000).

Student responses:
(A) : 31 students
(B) : 3 students
(C) : 5 students
(D) : 0 students