Determine the angle ϕ at which the applied force P should act on the pipe so that the magn...

Determine the angle ϕ at which the applied force P should act on the pipe so that the magnitude of P is as small as possible for pulling the pipe up the incline. What is the corresponding value of P? The pipe weighs W and the slope α is known. Express the answer in terms of the angle of kinetic friction, θ tan-1 µk.