Turning effects of forces 3 1. The problem statement, all variables and given/known data A ruler of an unknown mass is 52.0cm long. To find out its mass, you put a stone of 100g on the ruler 3.0cm from its end and balance the ruler on a sharp edge. The ruler is balanced when the supporting edge is 15.0cm from its end. Calculate the mass of the ruler. 2. Relevant equations I know that the force of the stone is 0.981N. But what do I have to do to find out the force pointing downward of the ruler, so that I can find the mass...?