JEE Main 2014 · 6 Apr · Shift 1, Physics question 6

For the conical pendulum, the angular momentum about the point of suspension, $\vec r\times m\vec v$, has constant magnitude ($r$, $v$ and the angle between them are fixed). But it is tilted from the vertical and turns round with the bob. Gravity and tension give a horizontal torque about that point, so $\vec L$ changes in direction but not in magnitude.