(a)[2]
Define the torque produced by a couple.
(b)
A wheel is held up by a pin P at its centre of gravity, as shown in Fig. 4.1. The wheel lies in a vertical plane. Its radius is $25\,\text{cm}$. Two parallel forces, each of $35\,\text{N}$, act on the rim of the wheel in the vertical directions shown in Fig. 4.1. Friction between the pin and the wheel is negligible.
(b(i))[2]
List two further forces that act on the wheel. State the direction of each force and where it acts.
(b(ii))[2]
Calculate the torque of the couple acting on the wheel from the given forces.
(b(iii))[1]
The resultant force on the wheel is zero. Explain, with reference to the four forces acting on the wheel, how it is possible for the resultant force to be zero.
(b(iv))[1]
State and explain if the wheel is in equilibrium.