Three spools A, B and C each having moment of inertia I= MR2/4 are placed on rough ground and equal force F is applied at positions as shown in the figures (a), (b) and (c). Then

For figure A and BIf k2 > Rx friction will act in backward direction otherwise in forward direction.For given spool K2=R24Fig.(a). Rx=R⋅R3=R23 friction forwardFig. (b). Rx=R⋅R5=R25 friction backwardIn figure (c) as force is below the diametric plane, hence friction backward.