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JEE Advanced2012PhysicsRotational MotionActual

A small mass m is attached to a massless string whose other end is fixed at P as shown in the figure. The mass is undergoing circular motion in the x-y plane with centre at O and constant angular speed . If the angular momentum of the system, calculated about O and P are denoted by L _ O and L _ P respectively, then

Options

  1. AL _ O and L _ P do not vary with time
  2. BL _ O varies with time while L _ P remains constant
  3. CL _ O remains constant while L _ P varies with time
  4. DL _ O and L _ P both vary with time

Correct answer

C. L _ O remains constant while L _ P varies with time

Step-by-step solution

For all locations of m the angular momentum of the mass m about O i.e., L_ o is m r² and is directed toward +z direction. The angular momentum of mass m about P i.e., L_ p is m v l and is directed for the given location of m as shown in the figure. For different location of m , the direction of L _ P remains changing.

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