The pilings for a bridge across a river that is 6 ft deep and flows at a maximum speed of 6 mph are made of wood poles 8 in. in diameter buried in the river bed. Estimate the bending moment at the river bed for a piling and discuss the accuracy of the calculation. A steel sphere of 0.25 in. diameter has a velocity of 200 ft/s at an altitude of 30,000 ft in the U.S. Standard Atmosphere. Calculate the drag force on this sphere.