A round disc of moment of inertia `I_2` about its axis perpendicular to its plane and passing through its centre is placed over another disc of moment of inertia `I_1` rotating with an angular velocity `omega` about the same axis. The final angular velocity of the combination of discs is.

Options

A. `((l_(1)+l_(2))omega_(1))/(l_(1))`
B. `(l_(1)omega_(1))/(l_(1)+l_(2))`
C. `omega_(1)`
D. `(l_(2)omega_(1))/(l_(1)+l_(2))`

Answer

B

Explanation

`l_(1)omega_(1)=(l_(1)+l_(2))omega_(2)`
`therefore omega_(2)=(l_(1)omega_(1))/(l_(1)+l_(2))`