Define the centre of gravity.
A uniform rod AB is fixed to a vertical wall at A. A string holds the rod horizontally by being attached at B and at point C, as shown in Fig. 3.1. The angle between the rod and the string at B is $50^{\circ}$. The rod has length $1.2\,\text{m}$ and weight $8.5\,\text{N}$. An object O of mass $M$ is suspended from the rod at B. The tension $T$ in the string is $30\,\text{N}$.
Use the resolution of forces to find the vertical component of $T$.
State the principle of moments in equilibrium.
Use the principle of moments and take moments about A to show that the weight of object O is $19\,\text{N}$.
Hence determine the mass $M$ for object O.
Use the concept of equilibrium to explain why a force has to act on the rod at A.