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Old May 11th 2017, 06:54 PM   #1
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Magnitude and direction of arm

Would like to know if this working is correct or not and help on part b?

I have for my answer of A) (after finding theta etc):

0 = ((12*9.81)*0.0365)+((1.5*9.81)*0.155)-(Fy*0.05)
Fy = (42.9678+2.2808)/0.05
Fy = 904.972N

F being brachialis group muscles:
F=Fy/cos(theta)
F = 904.972/cos(13.39)
F = 930.26N

direction from positive x axis:
90+13.39 = 103.39degrees

No idea where to go from here for part b
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Magnitude and direction of arm-brachialis.png  
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Old May 11th 2017, 07:11 PM   #2
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I assume the arm is in equilibrium (not moving)? Looks like a problem involving equilibrium and torque.
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Old May 11th 2017, 07:14 PM   #3
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I'm under the same assumption - it does say "slow arm curls" but without a statement of speed I've just assumed equilibrium
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Old May 11th 2017, 07:38 PM   #4
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It appears as though the briachilis muscle is attached a small distance from the elbow joint and I assume they are suggesting that the briachilis muscle is the primary and dominating support for the forearm. If I understand the question correctly the attachment of the briachlis muscle to the forearm is the pivot point. Therefore the force and torque on the elbow joint E exactly counterbalances the sum of the torque (force * distance * cosine angle between them) on the other side. Therefore the force on joint E will be roughly upward (opposite gravity) if my interpretation of the question is correct. Make sense?
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