# Homework Help: Shear Stress Problem

1. Apr 22, 2014

### M_J

1. The problem statement, all variables and given/known data

The force on a knee cartilage can cause a large force to deform it. The cartilage area is 11cm^2 and the shear modulus is 12MPa. Max force at impact is 904N at an angle of 12 degrees with the cartilage, through what angle (in degrees) will the cartilage be deformed?

2. Relevant equations

http://session.masteringphysics.com/problemAsset/1026529/6/yg.11.35.jpg

Shear modulus = Stress/Strain

Stress = F(perpendicular)/A

Strain = x/h

3. The attempt at a solution

Stress = 904sin(12)/11x10^-4

Strain = 0.0142

h=11x10-2 ??

angle = tan^-1(0.0142/11x10-2) = 7.4

This method appears a little wrong, is someone able to point out where I have gone wrong and how I should have got to the answer? Thanks! :-)

2. Apr 22, 2014

### SteamKing

Staff Emeritus
Your calculations are also units-free, which makes them even more difficult to follow.

3. Apr 22, 2014

### M_J

All units are SI, stress has units of Pa, strain is a ratio so has no units and h is measured in metres. My angle is in degrees.

I would be grateful if you were now able to help me with my answer! :-)

4. Apr 22, 2014

### Staff: Mentor

Your angle calculation is incorrect. You already have the shear strain, so why are you dividing by the area?

Chet

5. Apr 22, 2014

### M_J

Thanks, can you explain what I do need to do then please?

6. Apr 22, 2014

### M_J

Don't worry, I have done it now - thanks anyway!

7. Apr 22, 2014

### M_J

Thanks!

8. Apr 27, 2014

### bpennkast

what exactly did you do to change your original setup? i can't figure this one out