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JEE Main202117 Mar 2021Morning ShiftPhysicsRotational MotionActual

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 L A which lies in the positive z direction and the angular momentum of M about B is L B . The correct statement for th

Options

  1. AL A and L B are both constant in magnitude and direction
  2. BL B is constant in direction with varying magnitude
  3. CL B is constant, both in magnitude and direction
  4. DL A is constant, both in magnitude and direction

Correct answer

D. L A is constant, both in magnitude and direction

Step-by-step solution

We know, L → = m ( r → × v → ) Now with respect to   A , we always get direction of L → along + v e z -axis and also constant magnitude as mvr. But with respect to B , we get constant magnitude but continuously changing direction.

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