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