1. The problem statement, all variables and given/known data An octagon is on a table with no friction. There are two equal forces which are put on two faces of the octagon, one in direction of the north, the other in direction of the south-east. These forces are all 0,5 N. If the module of the acceleration is 0,3 m/s^2, what is the mass of the object. 2. Relevant equations Sum of Force of y = m * a in y Sum of Force of x = m a in x 3. The attempt at a solution I know that I must decompose my south-east forces and find its component. What I don't understand is how to find the components of the acceleration to be able to do my calculations. Could somebody give me a hint ?