7-2. The minimum
radius of curvature of a pole is estimated when the sportsman is performing a
pole vault. If the minimum radius of curvature of the pole is 4.2 m, and the
allowable bending stress is
,
determine the probability of failure. Given that the pole has a
diameter of 36 mm and its material has a Young’s modulus of
. Assume E and 
are independent. (Ans. 
)