on de problemas; razonamiento de estudiantes; ensenanza de la f´ isica; conocimiento declarativo; conocimiento pro- cedural The capacity for retaining the acquired knowledge of the students participating in one Physic course is analyzed as well as the ability to solve open problems that have a known solution. The analysis is focused to the degree of procedural and declarative knowledge; the last one was used using the categorization based in stages designed for analyzing simple written answers according with the standard methodology. From these results we inferred that the learning process of the students generate a routine semantic memory without meaningful semantic knowledge due to the absence of procedural work. This procedure favors a separation from the scientific teaching where the student is moved away from the kind of work made in the scientific environment.