Physics quiz question: rate of tropical rainforest area loss

Physics 205A Quiz 1, fall semester 2016
Cuesta College, San Luis Obispo, CA

A recent statistic[*] states that 80,000 acres of tropical rainforest are lost daily. An acre is defined as the area of a 66 ft × 660 ft plot of land, and 3.281 ft = 1 m. The average rate of rainforest area lost in square meters per hour is:
(A) 1.3×10⁷ m²/h.
(B) 4.4×10⁷ m²/h.
(C) 4.8×10⁸ m²/h.
(D) 1.6×10⁹ m²/h.

[*] scientificamerican.com/article/earth-talks-daily-destruction/.

Correct answer (highlight to unhide): (A)

The area lost in square meters per hour can be determined from converting the units from the given rate of 80,000 acres per day by setting up conversion factors such that unwanted units cancel (acres, hours) while desired units remain (square meters, seconds):

80,0000 acres/day = (80,0000 acres/day)·(1 acre/(66 ft)·660 ft))·(3.281 ft/1 m)·(3.281 ft/1 m)·(1 day/24 h),

80,0000 acres/day = 13,488,204.927 m²/h,

which to two significant figures, is 1.3×10⁷ m²/h.

Sections 70854, 70855, 73320
Exam code: quiz01bIR6
(A) : 33 students
(B) : 10 students
(C) : 7 students
(D) : 7 students

Success level: 58%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.60