STRESS (part I) *

1.	Draw a configuration in which the net force at the contact of two blocks is 10 N and the shear component is -5 N (don’t forget the sign convention).  What are the normal component and the angle of the net force relative to the normal vector of the block contact?  Draw and label all aspects of the problem.	Extra credit:  What is the other possible answer?

2.	If the area of contact between the two blocks of the previous problem is 1 square inch, what are the normal and shear stresses in pascals, bars, and psi?

3.	Assume that the crust of the Andes is 60 km thick, and that the density is 2.6 gm cm-3 at the top and 3.0 gm cm-3 at the base.  If the density varies linearly from top to bottom, derive an equation for the lithostatic pressure at any depth (z).  What is the lithostatic pressure at a depth of 30 km?  At the base?  Give the answers in MPa.

4.	In a sandstone consisting of spherical, perfectly sorted grains (assume closest packing), what is the stress concentration (relative to the nominal stress) at the grain contacts if the contact lengths are one tenth of the grain diameters?  Neglect friction and fluid pressure, and solve the problem by doing a force balance on one half of one grain, as shown below.

Extra credit:  Do problem 4 in 3D.