Even when the head is held erect, as in the figure below, its center of mass is

Question

Even when the head is held erect, as in the figure below, its center of mass is not directly over the principal point of support (the atlanto-occipital joint, point A). The muscles at the back of the neck should therefore exert a force to keep the head erect. That is why your head falls forward when you fall asleep in the class. If the head weighs 49 N, calculate the force exerted by the muscles, FM, using the information in the figure. F vector_M = Number N What is the force exerted by the pivot on the head, F_J? F vector_j= Number N

Explanation / Answer

As we know

net force must be 0 so

F3=49+Fm ...........(1)

writing torque equation about centre

Fm*(5.1+1.9) -F3*1.9=0

we got Fm=0.271*F3

putting in (1) we got

F3=67.25 N

Fm=18.22 N

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