The deltoid muscle is the main muscle that allows you to raise your arm or even

Question

The deltoid muscle is the main muscle that allows you to raise your arm or even hold it out. It is connected to the humerus of the upper arm. The person shown is holding his arm out horizontally with a 3.00kg weight in his hand. This weight is 60.0cm from the shoulder joint. His forearm (including his hand) has a mass of 2.30kg and is 34.0cm long; its center of mass is 43.0cm from the shoulder joint, measured along the arm. His upper arm is 26.0cm long and has a mass of 2.59kg ; its center of mass is 13.0cm from the shoulder joint. The deltoid muscle is attached to the humerus 15.0cm from the shoulder joint and makes a 14.0 degree angle with the humerus What is the tension in the deltoid muscle?

Explanation / Answer

The torque = force * distance to pivot point Weight: M1 = 3*9.8*0.6=17.64 Forearm: M2 = 2.3*9.8*0.43=9.69 Upper arm: M3 = 2.59*9.8*0.13=3.185 Muscle: M4 = F * 0.15 *sin(14 degree) Equilibrium: M4 = M1 + M2 + M3 =24.01 M4=24.01 Muscle: M4 = F * 0.15 *sin(14 degree) 24.01=F*0.036 => F =667 N

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