Brakes, static equilibrium problem is my Free Body Diagram correct?

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SUMMARY

The discussion focuses on calculating the minimal force P of the brakes during the stopping of a wheel, with the solution determined to be P=34.3 N. Participants emphasize the importance of accurately drawing Free Body Diagrams (FBD) for both the lever and the wheel to correctly analyze the forces involved. The distance "a" plays a crucial role in calculating moments, as it affects the friction force's moment about the lever's pivot point. The oversight of including the friction force (Fb) in the FBD was identified as a key error in the initial calculations.

PREREQUISITES
  • Understanding of Free Body Diagrams (FBD)
  • Knowledge of static equilibrium principles
  • Familiarity with moment calculations in physics
  • Basic grasp of forces and friction in mechanical systems
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  • Study the principles of static equilibrium in mechanical systems
  • Learn how to accurately construct Free Body Diagrams
  • Explore moment calculations and their applications in physics
  • Investigate the role of friction forces in dynamic systems
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This discussion is beneficial for physics students, mechanical engineers, and anyone involved in analyzing forces and moments in static equilibrium problems.

Femme_physics
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Homework Statement



Calculate minimal force P of the brakes during the stopping of the wheel.

[PLAIN]http://img823.imageshack.us/img823/6017/problemzy.jpg


Solution is P=34.3 [N]

Homework Equations



(Written on scan above)

The Attempt at a Solution



[PLAIN]http://img7.imageshack.us/img7/5720/problemtry.jpg

My great confusion is what is the purpose of the radius and what is the purpose of distance a? Are my equations and diagram even correct? I'm not getting the written result...
 
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Hi Dory! :smile:
Dory said:
...is my Free Body Diagram correct?

hmm … this is a very good example why it is very important to draw a good free body diagram …

in this case you must draw two diagrams … one for the lever, and one for the wheel

the relevance of the distance "a" is that when you take moments about the usual point for the lever, the friction force (unusally) will not have zero moment :wink:

start again :smile:​
 
Ah...got it... So I completely forgot the force Fb in my FBD! That's why I need that 0.05! Thanks :D
 
There it is...just for the record
 

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Dory said:
There it is...just for the record

Mazeltov! :biggrin:
 

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