JEE MAIN - Physics (2021 - 17th March Morning Shift - No. 9)
A mass M hangs on a massless rod of length l which rotates at a constant angular frequency. The mass M moves with steady speed in a circular path of constant radius. Assume that the system is in steady circular motion with constant angular velocity $$\omega$$. The angular momentum of M about point A is LA which lies in the positive z direction and the angular momentum of M about point B is LB. The correct statement for this system is :
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LA is constant, both in magnitude and direction
LB is constant in direction with varying magnitude
LB is constant, both in magnitude and direction
LA and LB are both constant in magnitude and direction
Explanation
Net force on M is towards A, hence torque is zero
about A.
$${\overrightarrow L _A} = \overrightarrow r \times \overrightarrow p $$
as $$r \bot p$$ so LA = constant
$${\overrightarrow L _A} = \overrightarrow r \times \overrightarrow p $$
as $$r \bot p$$ so LA = constant
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