# Person in a bus (accelerating system)

by pinsky
Tags: accelerating, person
 P: 97 Hy I'm having some issues about the Newtons third law. The image should represent a person in a bus with and the forces acting on them. The bus and the person are observed from outside the bus. The bus starts accelerating because of the force $F_{BUS MOVING}$. This force represent the resultant force of the friction between the bus and the ground, and the buses starting force. As a result, friction force $F_{P-BUS}$ occurs and it acts on the bus because of the mass of the person. As a reaction, a force of the same size but opposite direction acts on the person $F_{BUS-P}$ What is the sum of the forces on the bus? $F_{BUS MOVING}-F_{P-BUS}$ ? How would one calculate $F_{P-BUS}$ by knowing the mass of the person and $\mu$? Is this the solution? $F_{BUS MOVING}-F_{P-BUS}=F_{BUS-P}$ Since in this case, the bus and the person have the same value and orientation. That is what a observer from the street would see, right? Attached Thumbnails