A bob of mass m attached to an inextensible string of length l ⁡ is suspended from a vertical support.…

1. Angular momentum is conserved
2. Angular momentum changes in magnitude but not in direction
3. Angular momentum changes in direction but not in magnitude
4. Angular momentum changes both in direction and magnitude

Solution

$\tau =\text{mg}\times l\text{sin}\theta$. (Direction parallel to plane of rotation of particle)

                         

as $\tau$ is perpendicular to $\overrightarrow{\text{L}}$, direction of L changes but magnitude remains same.  

Asked in: JEE Main 2014 (06 Apr)

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