NEET 2010 Physics question
A circular disk of moment of inertia is rotating in a horizontal plane, about its symmetry axis, with a constant angular speed . Another disk of moment of inertia is dropped coaxially onto the rotating disk. Initially the second disk has zero angular speed. Eventually both the disks rotate with a constant angular speed . The energy lost by the initially rotating disc to friction is
Answer: (4)
Solution
No external torque acts on the two-disk system about the common axis, so angular momentum is conserved: , giving . Initial kinetic energy ; final kinetic energy $ = 12 +ω_ =
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