(a)[1]
Define the moment of a force in terms of turning effect.
(b)
A trapdoor is hinged at end A, as illustrated in Fig. 1.1. It has a length of $80\ \text{cm}$ and a weight of $75\ \text{N}$. Its mass is spread evenly along its length. A force $F$ acts at right angles to the trapdoor at end B so that the trapdoor is kept in equilibrium at an angle of $42^{\circ}$ to the horizontal.
(b(i))[2]
State the principle of moments in rotational equilibrium.
(b(ii))[1]
Calculate the component of the weight acting perpendicular to the trapdoor.
(b(iii))[2]
Calculate the magnitude of the force $F$.