Answer:
0.09 N
Explanation:
We are given that
Radius of disk,r=6 cm=
1 m=100 cm
B=1 T
Current,I=3 A
We have to find the frictional force at the rim between the stationary electrical contact and the rotating rim.





Torque due to friction

Where friction force=F


Substitute the values


It is an example of balanced force.
hope this helps. good luck