A laboratory balance uses a uniform beam XY XY\,XY of length 0.6 m which is pivoted at its centre.
A circular silicon wafer of diameter 120 mm and mass 80 g is placed on the beam so that its edge is exactly level with the end XXX. A calibration mass of M M\,M grams is suspended from the end Y Y\,Y by a light inextensible string.
The beam rests horizontally in equilibrium.
Find the value of MMM.
State one assumption you have made about the silicon wafer.