# Problem: A penny is placed at the outer edge of a disk (radius = 0.147 m) that rotates about an axis perpendicular to the plane of the disk at its center. The period of the rotation is 1.70 s. Find the minimum coefficient of friction necessary to allow the penny to rotate along with the disk.

###### FREE Expert Solution

In this problem, we consider the equation:

This can also be expressed as:

$\begin{array}{rcl}\mathbf{\mu }\overline{)\mathbf{m}}\mathbf{g}& \mathbf{=}& \overline{)\mathbf{m}}{\mathbf{\omega }}^{\mathbf{2}}\mathbf{R}\\ \mathbf{\mu }\mathbf{g}& \mathbf{=}& {\mathbf{\omega }}^{\mathbf{2}}\mathbf{R}\\ \mathbf{\mu }& \mathbf{=}& \frac{{\mathbf{\omega }}^{\mathbf{2}}\mathbf{R}}{\mathbf{g}}\end{array}$

83% (437 ratings) ###### Problem Details

A penny is placed at the outer edge of a disk (radius = 0.147 m) that rotates about an axis perpendicular to the plane of the disk at its center. The period of the rotation is 1.70 s. Find the minimum coefficient of friction necessary to allow the penny to rotate along with the disk.