A conical pendulum consists of a simple pendulum moving in a horizontal circle as shown. $C$ is the pivot. $0$ is the centre of the circle in which the pendulum bob moves and w the constant angular velocity of the bob. If $\overrightarrow {L} $ is the angular momentum about the axis $C_0$, then

Question

a) $\overrightarrow {L}$ is constant

b) only direction of $\overrightarrow {L}$ is constant

c) only magnitiude of $\overrightarrow {L}$ is constant

d) none of the above