Q 11-06-024JEE MainAIEEE 2007Easy
The angular momentum of a particle rotating with a central force is constant due to
Answer: (C) zero torque
A central force always acts along the line joining the particle to the centre, i.e. along $\vec{r}$. So its torque about the centre is $\vec{\tau} = \vec{r}\times\vec{F} = 0$.
With zero torque, $\dfrac{d\vec{L}}{dt} = 0$ and the angular momentum is conserved.
Solution by Sreeraj P, M.Sc Physics