Which of the following statements are correct?

1. Centre of mass of a body always coincides with the centre of gravity of the body. 
2. Centre of mass of a body is the point at which the total gravitational torque on the body is zero.
3. A couple on a body produce both translational and rotational motion in a body.
4. Mechanical advantage greater than one means that small effort can be used to lift a large load.

(b) and (d)

Centre of mass may or may not coincide with centre of gravity.

CoM is a point where whole mass is concentrated and hence, torque is zero.

Mechanical advantage : M = \(\frac{\text{output force}}{\text{input force}}\)

If M > 1, \(\Rightarrow \text{output} > \text{input}\)

Thus, less effort is required to lift large road.