In my graduation thesis we will investigate one task from the 35th State Competition in Physics for Stefan awards. The task was solved by pupils of the 8th grade on 11 April 2015. We will analyse the task that is in part B, which is an open ended type of task. The task is related to understanding the center of gravity, balance of forces, sketching forces, and torques. We will examine the answers of the students, to find out where common errors are, or if the background of errors is, for example, poor understanding of theory. However, since the task is divided into six sub-questions, we will also check, how often chain errors occur and at which parts. We will also check the objectivity of the tasks. I will gradethis task for all involved pupils and compare my own results with the published ones, to find out to what extent the grading at the State Competition is reliable, i.e., to estimate the “measuring error” of the grading at the competition for this task.