Physics clicker question: internal energy changes in an insulated system

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

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 14.33 (extended)

Students were asked the following clicker question (Classroom Performance System, einstruction.com) at the start of their learning cycle:

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 in internal energy once thermal equilibrium is reached?
(A) 50 g iron sample.
(B) 1000 g of water.
(C) (There is a tie.)
(D) (I'm lost, and don't know how to answer this.)

Sections 30880, 30881
(A) : 8 students
(B) : 11 students
(C) : 13 students
(D) : 1 student

This question was asked again after displaying the tallied results with the lack of consensus, with the following results. No comments were made by the instructor, in order to see if students were going to be able to discuss and determine the correct answer among themselves.

Sections 30880, 30881
(A) : 13 students
(B) : 6 students
(C) : 14 students
(D) : 0 students

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.

Pre- to post- peer-interaction gains:
pre-interaction correct =39%
post-interaction correct = 42%
Hake, or normalized gain = 5%