Arm problem, Static Equilibrium

AI Thread Summary
To solve for the force exerted by the deltoid muscle (Fm) required to hold up an outstretched arm weighing 3.3 kg, the calculation yields a result of 250 N. The equilibrium condition is established by balancing the torque due to the arm's weight against the torque produced by the deltoid muscle. For part b, to find the force (FJ) exerted by the shoulder joint, it is important to account for the cosine component of the deltoid force acting back into the joint. This requires applying the principles of static equilibrium and torque analysis. The discussion emphasizes the need to consider both sine and cosine components in the calculations to accurately determine the forces involved.
Bones
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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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