If you hold your arm outstretched with palm upward, the force to keep your arm from falling comes from your deltoid muscle. assume that the arm has mass 4 kg and the distances and angles shown in

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What force must the deltoid muscle provide to keep the arm in this position? By what factor does this force exceed the weight of the arm?If you hold your arm outstretched with palm upward, as in (Figure 1) , the force to keep your arm from falling comes from your deltoid muscle. Assume that the arm has mass 4 kg and the distances and angles shown in (Figure 1) . 

F=? 
F/w= ?

The answer is 339 N