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

[brittanyr]

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.

 

[haruspex]

weight supported by femur=0.9(85.0kg)= 76.5kg

That's a mass, not a weight. Weight is a force.

A=(pi)(0.02m)^2=0.1256m

What is 0.02²? What is (m)²?

 

[jbriggs444]

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.

 

[brittanyr]

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

 

[brittanyr]

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]

0.02^2 =0.4

0.4*3.14= 0.1256 ... 0.1255^2 =0.2512? Correct?

 

[haruspex]

0.02^2 =0.4

No.
Consult http://www.math.com/school/subject1/lessons/S1U1L5GL.html

And what will the units of the area be?

 

[brittanyr]

No.
Consult http://www.math.com/school/subject1/lessons/S1U1L5GL.html

And what will the units of the area be?

 

[brittanyr]

0.2*0.2=0.04
The unit would be Meters

 

[haruspex]

0.2*0.2=0.04

Yes, but you want 0.02*0.02

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.