Physics quiz question: density

Physics 5A Quiz 1, Fall Semester 2007
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problem 1.14

[3.0 points.] Density is the ratio of mass to volume. Ocean water has a density of 1.027 kg/m^3. What is the density of ocean water in units of g/cm^3?
(A) 1.027 x 10^(-3) g/cm^3.
(B) 1.027 g/cm^3.
(C) 10.27 g/cm^3.
(D) 1.027 x 10^3 g/cm^3.

Correct answer: (A)
1 kg = 1,000 g; 1 m = 100 cm.

Then 1.027 kg/m^3
= (1.027 kg/m^3)*(1,000 g/1 kg)*(1 m/100 cm)*(1 m/100 cm)*(1 m/100 cm)
=1.027 x 10^(-3) g/cm^3.

The incorrect response (C) has (1,000 g/1 kg), but only one conversion factor of (1 m/100 cm).

Student responses
Sections 0906, 0907
(A) : 18 students
(B) : 5 students
(C) : 16 students
(D) : 4 students