Variable friction on the Horizontal disc

A uniform disc is rotating with angular velocity $$\omega$$ and then it is gently placed horizontally on a rough horizontal surface having a coefficient of friction $$\mu$$ . The total time $$T$$ taken by disc to stop rotating completely can be expressed as

$$T\quad =\cfrac { a }{ b } \times \cfrac { \omega R }{ \mu g }$$.

Find The value of $$a\times b$$.

Details:

$$\bullet$$ 'a' and 'b' are Co-prime positive integers.

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