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$vii. A body is in neutral equilibrium when its centre of gravity:(a) is at its highest position(b) is at the lowest position(c) keeps its height if displaced(d) is situated at its bottom$

$4.12 Why a body cannot be in equilibrium due to single force acting on it?$

$4.6 The steering of a car has a radius 16 \mathrm{~cm} . Find the torque produced by a couple of 50 \mathrm{~N} . (16 \mathrm{Nm})$

$EXAMPLE 4.6 A uniform rod of length 1.5 \mathrm{~m} is placed over a wedge at 0.5 \mathrm{~m} from its one end. A force of 100 \mathrm{~N} is applied at one of its ends near the wedge to keep it horizontal. Find the weight of the rod and the reaction of the wedge.$

$4.3 Differentiate the following:(ii) torque and couple$

$EXAMPLE 4.1Find the resultant of three forces 12 \mathrm{~N} along x-axis 8 \mathrm{~N} making an angle of 45^{\circ} with x-axis and 8 \mathrm{~N} along y -axis.$

$4.8 Two blocks of masses 5 \mathrm{~kg} and 3 kg are suspended by the two strings as shown. Find the tension in each$