Answer to Question #281266 in Physics for Reinn

Question

A steel rod on a bridge must be made to withstand a pull of 5000 lbs. Find the diameter of

the rod assuming the factor safety of 5 and the ultimate stress of 64000 psi. (15 pts)

Answer 1

With the safety factor of 5, the rod must withstand a load of 5·5000=25000 lbs. The cross-sectional area of such a rod should be

$$A=F/\sigma=2.52·10^{-4}\text{ m}^2,\\\space\\ d=2\sqrt{\frac A\pi}=0.018 \text{ m},$$

or 1.8 cm, or 0.709 in.