Physics quiz question: same-temperature, different-mass heat exchange

Physics 205A Quiz 7, fall semester 2009
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Example 14.5

A 25 g iron sample and a 100 g iron sample are both at room temperature (25° C). The specific heat of iron is 0.44 kJ/(kg·K). When the 25 g iron sample and the 100 g iron sample are brought in contact with each other, heat is transferred from the __________ to the __________.
(A) 25 g iron sample; 100 g iron sample.
(B) 100 g iron sample; 25 g iron sample.
(C) (Both of the above choices.)
(D) (None of the above choices.)
(E) (Not enough information is given.)

Correct answer (highlight to unhide): (D)

Even though the 100 g iron sample has more internal energy than the 25 g iron sample, they are at the same temperature and thus will already be at thermal equilibrium when brought together in contact with each other, such that no heat will be exchanged between them.

Student responses
Section 72177
(A) : 0 students
(B) : 3 students
(C) : 2 students
(D) : 6 students
(E) : 0 students

Success level: 54%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.50