On a horizontal smooth plane there is a motionless vertical cylinder and disc A. A is connected to cylinder by thread AB. The disc is set in motion with initial velocity V. as shown. Then the angular momentum of the body is

Top view of cylinder is givenweight is balanced by Normal reactionresultant force= tension is initially acting at Btension  changes as it rotatestorque about point O  is not zero. τ=TR  in anticlockwise directiontherefore L of particle about O  is not conservedvelocity of particle changes continuously as direction changes.But KE remains constant as magnitude of velocity is constant