State the two conditions necessary for an object to be in equilibrium.

A metal rod of length $90 \mathrm{cm}$ has a disc of radius $24 \mathrm{cm}$ fixed rigidly at its centre, as shown. The assembly is pivoted at its centre.

Two forces, each of magnitude $30 \mathrm{N}$, are applied normal to the rod at each end to produce a turning effect on the rod. A rope is attached to the edge of the disc to prevent rotation. Calculate:

The torque of the couple produced by the $30 \mathrm{N}$ forces

A metal rod of length $90 \mathrm{cm}$ has a disc of radius $24 \mathrm{cm}$ fixed rigidly at its centre, as shown. The assembly is pivoted at its centre.

Two forces, each of magnitude $30 \mathrm{N}$, are applied normal to the rod at each end so as to produce a turning effect on the rod. A rope is attached to the edge of the disc to prevent rotation. Calculate:

The tension $\mathrm{T}$ in the rope.

State what is meant by the torque of a couple.

Three strings, $\mathrm{A},\mathrm{B} \& \mathrm{C}$, are attached to a circular ring, as shown in Figure $4.35$. The strings and the ring all lie on a smooth horizontal surface and are at rest. The tension in string $A$ is $8.0 \mathrm{N}$. Calculate the tension in strings $\mathrm{B} \& \mathrm{C}$.

This diagram shows a picture hanging symmetrically by two cords from a nail fixed to a wall. The picture is in equilibrium.

Explain what is meant by equilibrium.

This diagram shows a picture hanging symmetrically by two cords from a nail fixed to a wall. The picture is in equilibrium.

Draw a vector diagram to represent the three forces acting on the picture in the vertical plane. Label each force clearly with its name and show the direction of each force with an arrow.

This diagram shows a picture hanging symmetrically by two cords from a nail fixed to a wall. The picture is in equilibrium.

The tension in the cord is $45 \mathrm{N}$ and the angle that each. End of the cord makes with the horizontal is $50°$ Calculate:

The vertical component of the tension in the cord

This diagram shows a picture hanging symmetrically by two cords from a nail fixed to a wall. The picture is in equilibrium.

The tension in the cord is $45 \mathrm{N}$ and the angle that each. End of the cord makes with the horizontal is $50°$ Calculate:

The weight of the picture.