For drilling a hole with diameter of 12 % inches at Total vertical depth of 9500 ft the mud weight of 11.5 ppg and weight on bit of 66,000 lbf are required. The drill collar for drilling this section has OD of 8 inch and ID of 3 inch. Drill pipes of 5 inch OD with weight of 16.25 lb/ft made from Grade E steel are used. a) Determine the length of drill collar required for drilling in this section to prevent drill pipe buckling. b) Plot the axial forces of drill string and show on the diagram how many feet of drill pipes will be under compression and tension.