: Let the moment of inertial of disc I be and the angular speed of disc I be .

let the moment ofj inertia of disc II be and the angular speed of disc II be

Angular momentum of disc I be

and angular momentum of disc II be

The initial angular momentum of two discsis given by

When two discs are brought into contact face to face (one on top of other) and their axis of rotation coincide, the moment ofj inertia I ofj the system is equal to the sum of their individual moments ofinertia.

i.e., I =

let bethe final angular speed of the system.

The final angular momentum of the system is given by.

According to law of conservation of angular momentum, we get

…(i)

Kinetic energy of disc I is given by,

Kinetic energy of disc II is given by,

Initial kinetic energy of two discs is

Final kinetic energy of the system is,

(Using (i))

Loss in kinetic energy of the system.

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