A motorcycle rides on the vertical walls around the perimeter of a large circular room. The friction coefficient between the motorcycle tires and the walls is \mu. How does the minimum \mu needed to prevent the motorcycle from slipping downwards change with the motorcycle’s speed, s ?
Answer Choices
A. \mu \propto s^{0}
B. \mu \propto s^{-1 / 2}
C. \mu \propto s^{-1}
D. \mu \propto s^{-2}
E. none of these