Arm problem, Static Equilibrium

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SUMMARY

The forum discussion focuses on calculating the forces involved in holding an outstretched arm in static equilibrium. The first part of the problem involves determining the force exerted by the deltoid muscle (FM), which was calculated to be 250N using the equation tnet = mg(24m) - Fmsin15(0.12m) = 0. The second part of the problem requires calculating the force exerted by the shoulder joint (FJ) on the upper arm, taking into account the cosine component of the deltoid force. Specific values such as the mass of the arm (3.3 kg) and gravitational acceleration (9.8 m/s²) were utilized in the calculations.

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Homework Statement



(a) Calculate the magnitude of the force, FM, required of the "deltoid" muscle to hold up the outstretched arm shown in the figure. The total mass of the arm is 3.3 kg.

(b) Calculate the magnitude of the force FJ exerted by the shoulder joint on the upper arm
http://www.webassign.net/gianpse4/12-56.gif

Homework Equations





The Attempt at a Solution


I got part a:
tnet=mg(24m)-Fmsin15(0.12m)=0
Fmsin15(0.12m)=(3.3kg)(9.8m/s^2)(0.24m)
Fm=(3.3kg)(9.8m/s^2)(0.24m)/0.03106m
Fm=250N

How do I figure out Fj for part b?
 
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Consider the effect of the cosine component of the deltoid force back into the joint.
 

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