In the above question disc B is brought in contact with disc A, they acquire a common angular velocity in time t. The average frictional torque on one disc by the other during this periodis:

Options

A. `(2I omega)/(3t)`
B. `(9I omega)/(2t)`
C. `(9I omega)/(4t)`
D. `(3I omega)/(2t)`

Answer

A

Explanation

Let `omega_(1)` is the common angular velocity acquired by both the discs then using conservation of angular momentum we can write the following:
`I(2omega)+(2I)omega=(I+2I)omega_(1)impliesomega_(1)=(4omega)/(3)" ".....(i)`
Initial angular momentum of A: `L_(1)=I(2omega)=2Iomega`
Final angular momentum of A: `L_(2)=I(4omega//3)`
Angular impulse = Change in angular momentum
`taut=|L_(2)-L_(1)|impliestaut=(2Iomega)/(3)impliestau=(2Iomega)/(3t)`
Option (a) is correct.