This paper is part of a series of studies to improve the efficacy of online physics homework activities by integrating narrated animated solutions with mastery inspired exercises. In a clinical study using first- and second-year university students, the mastery group attempted question sets in four levels, with animated solutions between each attempt, until mastery was achieved on each level. This combined elements of formative assessment, the worked example effect, and mastery learning. The homework group attempted questions with immediate feedback and unlimited tries. The two groups took a similar amount of time to complete the activity. The mastery group significantly outperformed the homework group on a free response post-test that required students to show their work in solving near and far transfer problems.