A conical pendulum consists of a simple pendulum moving in a horizontal circle as shown in the figure. `C` is the pivot, `O` the centre of the circle in which the pendulum bob moves and `omega` the constant angular velocity of the bob. If `vecL` is the angular momentum about point `C`, then

Options

A. `vecL` is constant
B. only direction of `vecL` is constant
C. only magnitude of `vecL` is constant
D. none of the above

Answer

C

Explanation

The distance of `vecL` is perpendicular to the line joining the bob at point `C`. Since this line keeps changing its orientation is space, direction of `vecL` keeps changing, however, as `omega` is constant, magnitude of `vecL` remains constant.
Method 2 The torque about point is perpendicular to te angular momentum vector about point `C`. hence it can only change the directon of `L` and not its magnitude.