MIDI is an acronym that stands for Musical Instrument Digital Interface. It is a standard protocol that helps to connects musical instruments with computers and several hardware devices to communicate. It was invented in the 80's as a way to standardize digital music hardwares.
Due that the velocity is constant that means that friction force is equal to the force exert by you, otherwise the refrigerator will accelerate or decelerate and in both cases velocity will not be constant. So then the friction force between refrigerator and floor is 150 Newtons.
A chair at rest on the floor has two forces acting on it its own weight that pulls it downward and the floor pushing upward on the chair, both of these forces are acting on it but the net force is 0, so the chair remains at rest and its velocity stays at 0.
