Question

A force from the pelvic girdle acts on the base of the spine. what is the component of this force in the direction of the spine? (this large force is the cause of many back injuries).

Answer 1

155*L*cos30º 310*(½L)*cos30º - F*(⅔L)*sin12º = 0 

F*(⅔)*sin12º = [155 + 310*(½)]*cos30º 
F = 310*cos30º/[(⅔)*sin12º] = 1.9*10^3 N 
The force along the length of the spine is the sum of force components along the spine from the three forces 

310*sin30º + 155*sin30º + 1900*cos12º = 2.1*10^3 N