## College Physics (4th Edition)

The center of mass of sphere A is at the center of sphere A, and the center of mass of sphere B is at the center of sphere B. Let $d$ be the distance between the two centers. Let $5M$ be the mass of sphere A and let $M$ be the mass of sphere B. We can find the position of the center of mass from the center of sphere A along the straight line joining the centers. $x_{cm} = \frac{(5M)(0)+(M)(d)}{5M+M} = \frac{d}{6}$ Measured from sphere A's center, the center of mass of the system is $\frac{1}{6}$ of the distance along the straight line joining the two centers. The correct answer is: (c) inside sphere A somewhere on the line joining the centers.