The pipe is stuck in the ground so that when it is pulled upward the frictional force along its length varies linearly from zero at B to fmax (force/length) at C. Determine the initial force P required to pull the pipe out and the pipe’s elongation just before it starts to slip. The pipe has a length L, cross-sectional area A, and the material from which it is made has a modulus of elasticity E. (9-17).