Abookshelf is at rest in a room. a force of 35.0 newtons is applied to a bookshelf. if the floor imparts a frictional force of 2.90 newtons, what is the net force acting on the bookshelf?

The net force (Fn) acting on the bookshelf is the difference between forces that are acting to it in opposite directions. In the given above, the frictional force, 2.90 N, always acts opposite to the force applied to it, 35 N.
 
                                       Fn = 35 N - 2.90 N = 32.1 N

Thus, the net force acting to the bookshelf is 32.1N. 

The answer is b.the gaseous state is electrically positive, while the plasma state is electrically negative.