When an arm is held outstretched with palm upward, the force to keep the arm fro

Question

When an arm is held outstretched with palm upward, the force to keep the arm from falling comes from the deltoid muscle. Assume that the arm has mass 5.0 kg , that the deltoid is applying its force at 15 at a distance L1 = 15 cm , and that the arm's center of gravity is at a distance L2 = 41 cm  as shown in (Figure 1) .

Part A Answer is 517 N (What force must the deltoid muscle provide to keep the arm in this position?)

Part B

By what factor does this force exceed the weight of the arm? *** Answer is not 13.24

Explanation / Answer

m = 5.0 kg

L1 = 15 cm = 0.15 m

L2 = 41 cm = 0.41 m

A) Fm*sin*L1 = m*g*L2

Fm*sin15*15 = 5*9.8*41 Fm = 517 N

B) Weight = W = 5*9.8 = 49 N

Then Fm/W = 10.6

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