Out of the following which one is an example of dynamic equilibrium ?

(1) Moon revolving around the earth
(2) A pebble fixed at the end of a string whirling in a circular path
(3) An aeroplane moving at a constant height
(4) A beam balance balanced in a horizontal position.

1. (3) and (4)
2. (1), (2) and (3)
3. (1) and (2)
4. (1) and (3)

State the condition when on applying a force, a body has:

(a) translational motion

(b) rotational motion.

Write the expression for the moment of force about a given axis.

State one way to reduce the moment of a given force about a given axis of rotation.