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QJEEM21Ph22f5: JEE Main 2021 Physics - Class 11 JEEM21Ph22f5 Solution: A mass M hangs on a massless rod of length l which rotates at a …

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 ω. 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 :

JEE Main 2021 (Online) 17th March Morning Shift Physics - Rotational Motion Question 107 English

Multiple Choice Options

  • A LA is constant, both in magnitude and direction
  • B LB is constant in direction with varying magnitude
  • C LB is constant, both in magnitude and direction
  • D LA and LB are both constant in magnitude and direction

Step-by-Step Verified Solution

Net force on M is towards A, hence torque is zero about A.

L→A=r→×p→

as r⊥p so LA = constant

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