A man uses 1930J of energy while lifting a 20K mass up 7.5 meters. What is the percent of efficiency?

In Figure 18.9, the ground wire is first removed, then the rod. This leaves a positive charge on the sphere. If you remove the rod first and then remove the ground wire, there will be no charge left on the sphere. When the rod is removed, the repulsive force caused by the presence of the rubber rod no longer exists. As the wire is still attached, free electrons enter the sphere from the ground until the sphere is neutral again.