Define the moment of a force.
Fig. 4.1 shows a device used to lift heavy loads. A uniform metal beam AB is hinged to a vertical wall at A. The beam is held by a wire joining end B to the wall at C. The beam is at an angle of $30^\circ$ to the wall and the wire is at an angle of $60^\circ$ to the wall. The beam is $2.8\,\text{m}$ long and has a weight of $500\,\text{N}$. A load of $4000\,\text{N}$ hangs from B. The wire tension is $T$. The beam is in equilibrium. By taking moments about A, show that $T$ is $2.1\,\text{kN}$.
Calculate the vertical component $T_v$ of the tension $T$.
State and explain why $T_v$ is not equal to the combined load and weight of the beam even though the beam is in equilibrium.
Fig. 4.1 shows a lifting arrangement for heavy loads. A uniform metal beam AB is hinged to a vertical wall at A. A wire connects B to the wall at C and supports the beam. The beam is inclined at $30^\circ$ to the wall, while the wire is inclined at $60^\circ$ to the wall. The beam is $2.8\,\text{m}$ long and has a weight of $500\,\text{N}$. A load of $4000\,\text{N}$ is suspended from B. The wire has tension $T$. The beam is in equilibrium.