Rotational dynamics/Rigid objects in equilibrium

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SUMMARY

The discussion focuses on solving a rotational dynamics problem involving rigid objects in equilibrium. The key equation derived is 0 = (0.025)(M) + (0.15)(22) - (0.3)(111), leading to the conclusion that M equals 1200N. The participant highlights confusion regarding the direction of the M force and its representation in the problem. The final answer aligns with a provided multiple-choice option of 1.2X10^3 N, confirming the solution's validity.

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  • Understanding of rotational dynamics and equilibrium principles.
  • Familiarity with torque calculations (torque = force x length of lever arm).
  • Knowledge of net force equations in physics.
  • Ability to interpret free-body diagrams accurately.
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This discussion is beneficial for physics students, educators, and anyone involved in mechanical engineering or biomechanics, particularly those dealing with problems related to rotational dynamics and equilibrium.

giant016
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Homework Statement



physics.jpg


Homework Equations


Net force of the Y vector: -F1 + F2 - weight = 0


The Attempt at a Solution



I tried to solve the equation thinking that m could = torque (torque=force X length of lever arm) but I couldn't figure out how to fit in that .025m spot in between the joint and the muscle. Not sure if the equation provided will really help. Any help is appreciated!
 
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The question is tricky because the M force is drawn in the wrong direction. The M force is the blue arrow up, not a black arrow going right. Put an equation equal to 0 where clockwise moments are positive and counterclockwise are negative
0 = (0.025)(M) + (0.15)(22) - (0.3)(111)
M = 1200N

That doesn't seem right. That's equivalent to 122kg, resting on 1 muscle.
 
ShawnD said:
The question is tricky because the M force is drawn in the wrong direction. The M force is the blue arrow up, not a black arrow going right. Put an equation equal to 0 where clockwise moments are positive and counterclockwise are negative
0 = (0.025)(M) + (0.15)(22) - (0.3)(111)
M = 1200N

That doesn't seem right. That's equivalent to 122kg, resting on 1 muscle.

We have an answer sheet (it's a multiple choice question) and one of the answers is 1.2X10^3, and your equation makes sense, so...Thanks! I'm on some other forums (mostly car junk) and I've never gotten an answer that quick!
 

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