Justify,giving proper reasoning,whether the work done in the following case is positive or negative: Work done by the resistive force of air on a vibrating pendulum in bringing it to rest.

(NEGATIVE) The work done by the resistive force of air on a vibrating pendulum is negative.
This is because the resistive force of air (air resistance) always acts in a direction opposite to the direction of the motion of the pendulum.
Since the angle between the force and the displacement is $180^{\circ}$,the work done $(W = F \cdot s \cdot \cos(180^{\circ}))$ results in a negative value.