Static Equilibrium of deltoid muscle

AI Thread Summary
The discussion focuses on calculating the forces involved in holding an outstretched arm, specifically the force exerted by the deltoid muscle (Fm) and the shoulder joint (FJ). The total mass of the arm is given as 3.3 kg, leading to a weight force of 32.2 N. The initial calculations for Fm, including a scenario with an 8.5 kg weight in the hand, resulted in a force of 1644 N. When considering the scenario without additional weight, the recalculated force Fm is 250 N. The participant seeks guidance on how to determine the force exerted by the shoulder joint (FJ) for the second part of the problem.
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Homework Statement


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. Then, 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


We did a problem similar to this in class, but there was a 8.5kg object in the hand.
X direction:
Fjcos(theta)-Fmcos15=0

Y direction: Force of weight=32.2N
-Fjsin(theta)+Fmsin15 Force of object=83.3N
-32.3N-83.3N=0

tnet=Fm(0.12m)(sin15)-32.3N(0.24m)(sin90)-83.3N(0.52m)(sin90)=0
Fm=1644N

How would you this problem change is there is no weight in the hand like the above problem suggests?
 
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If there was no weight, you would not include the force of gravity from that weight or the torque caused by that force in your calculations.
 
Does this mean I just leave it out or do I alter the equation in some way?
 
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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