A wheel and motor assembly is connected by a rigid massless rod to a frictionless pivot. See the attached
Figure. The angle "theta" between the wheel's axis and the connecting rod is fixed.
If the motor is applying a torque "tau" to the wheel, and the wheel radius is "r", what is the magnitude and direction of the floor's friction force on the bottom of the wheel? Assume that the torque is small enough so that the wheel is not moving.