Question

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 the constant angular velocity of the
bob. If $\stackrel{\rightharpoonup }{L}$ is the angular momentum about point C, then

• A. $\stackrel{\rightharpoonup }{L}$ is constant
• B. Only direction of $\stackrel{\rightharpoonup }{L}$is constant
• C. Only magnitude of $\stackrel{\rightharpoonup }{L}$is constant
• D. Both magnitude and direction of $\stackrel{\rightharpoonup }{L}$ changes

Answer 1

The correct option is C Only magnitude of $\stackrel{\rightharpoonup }{L}$is constant

The direction of $\stackrel{\rightharpoonup }{L}$ is perpendicular to the line joining the bob to point C. Since this line keeps changing its orientation in space, direction of $\stackrel{\rightharpoonup }{L}$ keeps changing however as wis constant, magnitude of $\stackrel{\rightharpoonup }{L}$ remains constant.