The Interactive Physics Course on the Internet is an electronic book in which we have enhanced interactivity by means of 124 applets embedded into the HTML documents. These applets are simulations, computer experiments, problems, etc. This article deals with problems because problem-solving is an essential part of the teaching of Physics at undergraduate level. Unlike textbooks in which the information required to solve the problem is provided in the problem statements, some applets of the Interactive Physics Course require the students to observe an animation and sometimes make measurements of relevant parameters. With these applets we intend to help them to develop more expert problem-solving strategies, and to encourage them to solve problems.