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 3.45kg weight in his hand. This weight is 61.1cm from the shoulder joint. His forearm (including his hand) has a mass of 2.3kg and is 34.1cmlong; its center of mass is 41.8cm from the shoulder joint, measured along the arm. His upper arm is 26.6cmlong and has a mass of 2.53kg ; its center of mass is14.1cm from the shoulder joint. The deltoid muscle is attached to the humerus 13.6cm from the shoulder joint and makes a 14? angle with the humerus.

a) What is the tension in the deltoid muscle?

b) If the person was using wrist wieghts instead of one in his hand, what would be the tension in the deltoid muscle then? Let the new position of the weights be 50.09cm from the shoulder joint.

Explanation / Answer

Fdeltoid*0.136*sin14 = (3.45*9.8*0.611)+(2.3*9.8*0.418)+(2.53*9.8*0.141)

Fdeltoid = 1020.5 N

part b)

Fdeltoid*0.136*sin14 = (3.45*9.8*0.509)+(2.3*9.8*0.418)+(2.53*9.8*0.141)

Fdeltoid = 915.67 N

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