The problem we are dealing with in this investigation links cognitive and affective domains. The importance of studying the emotion in relation to problem solving in particular, has much to do with the impact of this factor and how it affects students' performance regarding their relationship with the discipline and their problem-solving ability, which results in academic failure. The aim of this investigation is to recognize the expressions of emotions during the process of understanding the modelling of the mathematical object of lineal function. In order to do so, a descriptive study was designed with qualitative methodology which was applied to third year students in secondary education from the Metropolitan Region of Santiago, Chile. A learning situation with the objective of solving a mathematical modelling problem was put into place, having previously carried out an experiment with a spring which was complemented by case studies. The results show that the effective factors which come into play in the students' learning of mathematics were very varied, but mostly they demonstrate that emotions and academic performance are directly related to each other.