I was told here that in Case A, the torque is equal to zero. I'm not really seeing that. I know torque is equal to rFsin[tex]\theta[/tex]. If I draw a vector from the rotation point (the very center of the spool) to the point where the force is being applied, I get that the force and r are perpendicular, so sin[tex]\theta[/tex]=1. Where am I going wrong? I was told that the torque in case B is rF, which I can clearly see by the same reasoning.

Question 2:

For both cases, I was told the net force and net torque on the system is 0. The system is considered to be both of the objects. If someone could explain this I'd appreciate it.

Thanks.