MultipleConcept Example 7 deals with the concepts that are important in this problem. A penny is placed at the outer edge of a disk (radius = 0.137 m) that rotates about an axis perpendicular to the plane of the disk at its center. The period of the rotation is 1.56 5. Find the minimum coefcient of friction necessary to allow the penny to rotate along with the disk. #5 = Number Units v