Physics quiz question: internal energy changes in an insulated system

Physics 205A Quiz 7, Spring Semester 2009
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Example 14.3

[3.0 points.] A 50 g iron sample at 75° C is placed into 1000 g of room temperature water (25° C), in a container that is insulated from the environment. Which component of this isolated system had the greatest change (increase or decrease) in internal energy once thermal equilibrium is reached?
(A) 50 g iron sample.
(B) 1000 g of water.
(C) (There is a tie.)
(D) (Not enough information is given.)

Correct answer: (C)

In this isolated system, the heat given up by the iron sample must be exactly equal to the heat taken in by the water. Thus the amount of internal energy changes of both components of this system must be equal. (This was asked in a nearly identical form as a clicker question earlier during this same semester.)

Student responses
Sections 30880, 30881
(A) : 14 students
(B) : 4 students
(C) : 20 students
(D) : 1 student

"Difficulty level": 51%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.33