  In this companion paper, we explore the use of isomorphic problem pairs
(IPPs) to assess introductory physics students' ability to solve and
successfully transfer problem-solving knowledge from one context to another in
mechanics. We call the paired problems "isomorphic" because they require the
same physics principle to solve them. We analyze written responses and
individual discussions to a range of isomorphic problems. We examine potential
factors that may help or hinder transfer of problem-solving skills from one
problem in a pair to the other. For some paired isomorphic problems, one
context often turned out to be easier for students in that it was more often
correctly solved than the other. When quantitative and conceptual questions
were paired and given back to back, students who answered both questions in the
IPP often performed better on the conceptual questions than those who answered
the corresponding conceptual questions only. Although students often took
advantage of the quantitative counterpart to answer a conceptual question of an
IPP correctly, when only given the conceptual question, students seldom tried
to convert it into a quantitative question, solve it and then reason about the
solution conceptually. Misconceptions associated with friction in some problems
were so robust that pairing them with isomorphic problems not involving
friction did not help students discern their underlying similarities.
Alternatively, from the knowledge in pieces perspective, the activation of the
knowledge resource related to friction was so strongly and automatically
triggered by the context, which is outside the conscious control of the
student, that students did not look for analogies with paired problems or other
aids that may be present.
