-b Fm A C W X ¦Y
The forces acting on the arm of an athlete doing shoulder exercises are shown in the figure. The athlete holds his arm at an angle of β = 30° with the horizontal axis . Point O represents the axis of rotation in the shoulder joint, point A represents the connection point of the deltoid muscle to the humerus, point B represents the center of gravity of the arm, and point C represents the application point of the force acting on the hand. The distances between the rotation axis (O point) of the shoulder joint and the points A, B and C are a=22 cm , b =33 cm and c= 60 cm , respectively . A force of F= 120 N, which makes an angle of γ=30° with the vertical from the point C, acts on the athlete's hand . Weight of the athlete's armW= 80 N. The direction of application of the Fm muscle force makes an angle of α=20° with the longitudinal axis of the arm. According to this;
a) Calculate the muscle strength F M
b) Calculate the angle θ of the joint reaction force F J with the horizontal.
c) Calculate the FJ joint reaction force .
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