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

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The discussion focuses on calculating the compression of a femur, emphasizing the distinction between mass and weight, where weight is defined as a force. Participants highlight the importance of understanding concepts like stress, strain, and Young's modulus, suggesting that foundational knowledge is necessary for accurate calculations. There is confusion regarding the area calculation, specifically squaring the radius correctly and applying appropriate units. Clarifications are provided on the correct mathematical operations and the significance of using consistent units throughout the calculations. The conversation underscores the need for a solid grasp of physics principles to solve the problem effectively.
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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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