Three identical metal spheres are labelled a, b and c. initially, a has charge +5q/2, b has charge +3q/2 and c has charge -4q. b is first touched to a, removed, then touched to c and removed. finally, all three spheres are brought into contact with one another simultaneously (a touching b while b is also touching c) before once again being separated. what is the final electric charge on sphere b?

In an old-fashioned amusement park ride, passengers stand inside a 3.0-m-tall, 5.0-m-diameter hollow steel cylinder with their backs against the wall. the cylinder begins to rotate about a vertical axis. then the floor on which the passengers are standing suddenly drops away! if all goes well, the passengers will “stick” to the wall and not slide. clothing has a static coefficient of friction against steel in the range 0.60 to 1.0 and a kinetic coefficient in the range 0.40 to 0.70. part a what is the minimum rotational frequency, in rpm, for which the ride is safe? express your answer using two significant figures. f f = rpm