Homework Help: Engineering problem (uses stress, strain, Young's Modulus)

1. Feb 10, 2010

twostep08

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

2. As engineers, we wish to use a metal bar as a support arm on a crane. The bar has a
Young’s Modulus of 3x106psi . Assuming the rod will need to be 3ft long. Answer the
following questions…
a)If the crane is designed so that the
maximum tensile force on the rod is predicted to be
160,000 lbs, what should the cross sectional area of the rod
be to have a strain less than 0.001? _________
b) There was an accident at the worksite and the crane needs to lift a
600,000 lbs boulder to rescue some workers. If the bar has an Ultimate Tensile Strength
of 6400psi and the bar supports all of the weight , how much can the
crane actually lift?
__________

2. Relevant equations
stress= force/ area (sq.in.)
UTS= weight where a rod breaks/cross sectional area
Strain=extension/original length
YM=stress applied/strain induced

3. The attempt at a solution

I tried everything seemling, but I cant figure out where to plug in everything to get an answer that makes sense. I would really appreciate it if someone can walk me through it (I'm really good at math, but ive never taken physics, and this is my first engineering class, so I am understandably a little lost)

thanks alot