A Hoop Is Rolling (Without Slipping) on the Ground

Multiple Choice

A hoop is rolling (without slipping) on the ground. Its axle travels at 20 m/s with respect to the ground. There are two angular positions on the rim where the instantaneous speed (with respect to the ground) is 20 m/s. The two angular positions are separated by an angle of

A) 30^o.
B) 60^o.
C) 90^o.
D) 120^o.
E) 180^o.