Question

kmarks People Window Help Quiz: 95 x 0 Mail - S Power R Cheapo Cheap 0618/quizzes/19056/take Questions pus 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). The muscles in the back of the neck must therefore exert a force to keep it erect. That is why your head falls forward when you fall asleep in class. If the perpendicular distance between the line of action for the weight of the head and the pivot point is rwi = 3.3 cm and the perpendicular distance between the line of action for the force the muscles exert on the head and the pivot point is rmi = 5.3 cm, determine the force which must be exerted by the muscles in your neck. (Assume the weight of the head is 55 N.) overview...ing A

Answer 1

Take moment about the support

$\sum M=0$

$F_{M}*r_{M}-W*r_{W}=0$

$F_{M}*r_{M}=W*r_{W}$

$F_{M}=\frac{W*r_{W}}{r_{M}}$

$F_{M}=\frac{55N*0.033m}{0.053m}$

ANSWER: ${\color{Red} F_{M}=34.245N}$

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