Physics: How much is this person's femur compressed?

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Homework Help Overview

The discussion revolves around calculating the compression of a femur under a specific weight, involving concepts from mechanics and material science, such as stress, strain, and Young's modulus.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants explore the relationship between mass and weight, question the calculations of area, and discuss the relevance of physical principles like Hooke's law and Young's modulus. There is also confusion regarding the correct squaring of measurements and units.

Discussion Status

The conversation is ongoing, with participants providing clarifications and corrections regarding calculations and concepts. Some guidance has been offered regarding the need to understand relevant physical principles, but no consensus has been reached on the specific calculations or interpretations.

Contextual Notes

There appears to be some missing information regarding parameters necessary for the calculations, and participants are referencing course material that may not have been fully covered.

brittanyr
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Homework Statement
A 89.0 kg person stands on one leg and 90% of the weight is supported by the upper leg connecting the knee and hip joint-the femur. Assuming the femur is 0.650 m long and has a radius of 2.00 cm, by how much is the bone compressed?
Relevant Equations
weight supported by femur=0.9(85.0kg)= 76.5kg
L= 0.650m
A=(pi)(0.02m)^2=0.1256m
Thats how far I got with my equation. Help me please.
 
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brittanyr said:
weight supported by femur=0.9(85.0kg)= 76.5kg
That's a mass, not a weight. Weight is a force.
brittanyr said:
A=(pi)(0.02m)^2=0.1256m
What is 0.022? What is (m)2?
 
In your course work, have they been talking to you about Hooke's law, stress, strain, deflection, Young's modulus and such? If not, we will need to start from first principles and notions of relevant proportionality.

Google can easily find a relevant parameter not given in the problem statement here.
 
jbriggs444 said:
In your course work, have they been talking to you about Hooke's law, stress, strain, deflection, Young's modulus and such? If not, we will need to start from first principles and notions of relevant proportionality.

Google can easily find a relevant parameter not given in the problem statement here.
Yes. We are using stress, strain, and Young’s modulus
 
haruspex said:
That's a mass, not a weight. Weight is a force.

What is 0.022? What is (m)2?
0.02^2 =0.4
 
brittanyr said:
0.02^2 =0.4
0.4*3.14= 0.1256 ... 0.1255^2 =0.2512? Correct?
 
0.2*0.2=0.04
The unit would be Meters
 
  • #10
brittanyr said:
0.2*0.2=0.04
Yes, but you want 0.02*0.02
brittanyr said:
The unit would be Meters
The metre is a unit of length. You are calculating an area. I gave you the hint in post #2. You had (0.02m)2. You (inaccurately ) squared the 0.02 but you left the m as just m.
 

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